<PAGE>

As filed with the Securities and Exchange Commission on December 20, 1999.
                                             Registration No.333-
--------------------------------------------------------------------------------

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549
                                   --------

                                   FORM S-8
            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                                   --------

                      NATIONAL ENVIRONMENTAL SERVICE CO.
            (Exact name of registrant as specified in its charter)

           Oklahoma                                        73-1296420
(State or other jurisdiction of                        (I.R.S. employer
incorporation or organization)                         identification no.)


                             12331 East 60th Street
                             Tulsa, Oklahoma  74146
          (Address of principal executive offices including zip code)

          National Environmental Service Co. 1994 Employee Stock Plan
      National Environmental Service Co. 1994 Director Stock Option Plan
    National Environmental Service Co. Employees Savings Trust 401(k) Plan
                           (Full title of the plan)
                                   --------

                               Larry G. Johnson
                            12331 East 60th Street
                            Tulsa, Oklahoma  74146
                    (Name and address of agent for service)

 Telephone number, including area code, of agent for service:  (918) 250-2227

                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------
                                                              Proposed         Proposed
                                                              maximum           maximum         Amount of
Title of securities                       Amount to be     offering price      aggregate     registration fee
to be registered                          registered(1)       per share     offering price
------------------------------------------------------------------------------------------------------------------
<S>                                     <C>                <C>              <C>              <C>
1994 Employee Stock Plan
Common Stock, $.01 par value
(Outstanding options)                   257,000 shares          $2.494 (2)   $  641,000 (2)
------------------------------------------------------------------------------------------------------------------
1994 Employee Stock Plan
Common Stock, $.01 par value
(Options available for future grant)    516,735 shares          $2.875 (3)   $1,485,613 (3)
------------------------------------------------------------------------------------------------------------------
1994 Director Stock Option Plan
Common Stock, $.01 par value
(Options available for future grant)    150,000 shares          $2.875 (3)   $  431,250 (3)
------------------------------------------------------------------------------------------------------------------
Employees Savings Trust 401(k)
Common Stock, $.01 par value            120,000 shares          $2.875 (3)   $  345,000 (3)
------------------------------------------------------------------------------------------------------------------
Total Registration Fee                                                       $2,902,863       $  767.00
==================================================================================================================
</TABLE>

(1) In addition, pursuant to Rule 416(c) under the Securities Act of 1933, this
Registration Statement also covers an indeterminate amount of interests to be
offered or sold pursuant to the Employees Savings Trust 401(k).

(2) The computation is based upon the weighted average exercise price per share
of $2.494 as to outstanding options to purchase 257,000 shares under the 1994
Employee Stock Plan.

(3) Estimated solely for the purposes of calculating the registration fee
pursuant to Rule 457(h), on the basis of the average of the bid and ask price
for the Common Stock as reported on the Nasdaq SmallCap Market on December 14,
1999.
<PAGE>

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

Information required by Part I of Form S-8 to be contained in the Section 10(a)
Prospectus is omitted from this Registration Statement in accordance with Rule
428 under the Securities Act of 1933, as amended (the "Securities Act"), and the
Note to Part I of Form S-8.


<PAGE>

                                    PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.   Incorporation of Documents by Reference.

     The following documents and information previously filed by the Registrant
with the Securities and Exchange Commission are incorporated by reference in
this Registration Statement:

     (1)  The Registrant's Annual Report on Form 10-KSB for the year ended
          December 31, 1998, as amended by Amendment No. 1 on Form 10-KSB/A
          filed with the Commission on October 8, 1999;

     (2)  The Registrant's Quarterly Reports on Form 10-QSB for the quarters
          ended March 31, 1999, June 30, 1999 and September 30, 1999;

     (3)  The Registrant's Current Report on Form 8-K filed with the Commission
          on May 21, 1999, as amended by Amendment No. 1 on Form 8-K/A filed
          with the Commission on July 21, 1999;

     (4)  The Registrant's Current Report on Form 8-K filed with the Commission
          on September 22, 1999, as amended by Amendment No. 1 on Form 8-K/A
          filed with the Commission on November 12, 1999; and

     (5)  The description of the Registrant's Common Stock contained in the
          Registration Statement on Form 8-A declared effective by the
          Commission on September 13, 1994, and including any amendment or
          report heretofore or hereafter filed for the purpose of updating the
          description of the Registrant's Common Stock contained therein.

     In addition, all documents subsequently filed by the Registrant or the
Employees Savings Trust 401(k) Plan pursuant to Sections 13(a), 13(c), 14 and
15(d) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"),
prior to the filing of a post-effective amendment which indicates that all
securities offered hereby have been sold or which deregisters all securities
offered hereby then remaining unsold, shall be deemed to be incorporated by
reference in this Registration Statement and to be a part hereof from their
respective dates of filing. Any statement contained in a document incorporated
by reference shall be deemed to be modified or superseded for purposes of this
Registration Statement to the extent that a statement contained in any other
subsequently filed incorporated document modifies or supersedes such statement.
Any such statement so modified or superseded shall not be deemed, except as so
modified or superseded, to constitute a part of this Registration Statement.

Item 4.   Description of Securities.

          Not applicable.

                                      II-1
<PAGE>

Item 5.   Interests of Named Experts and Counsel.

          Not applicable.

Item 6.   Indemnification of Directors and Officers.

     The Registrant's By-Laws provide that each person who was or is made a
party to, or is involved in, any action, suit or proceeding by reason of the
fact that he or she was a director or officer of the Registrant (or was serving
at the request of the Registrant as a director, officer, employee or agent for
another entity) will be indemnified and held harmless by the Registrant, to the
full extent authorized by the Oklahoma General Corporation Act.

     Under Section 1031 of the Oklahoma General Corporation Act, a corporation
may indemnify a director, officer, employee or agent of the corporation against
expenses (including attorneys' fees), judgments, fines and amounts paid in
settlement actually and reasonably incurred by him or her if he or she acted in
good faith and in a manner he or she reasonably believed to be in or not opposed
to the best interests of the corporation and, with respect to any criminal
action or proceeding, had no reasonable cause to believe his or her conduct was
unlawful. In the case of an action brought by or in the right of a corporation,
the corporation may indemnify a director, officer, employee or agent of the
corporation against expenses (including attorneys' fees) actually and reasonably
incurred by him or her if he or she acted in good faith and in a manner he or
she reasonably believed to be in the best interests of the corporation, except
that no indemnification shall be made in respect of any claim, issue or matter
as to which such person shall have been adjudged to be liable to the corporation
unless a court finds that, in view of all the circumstances of the case, such
person is fairly and reasonably entitled to indemnity for such expenses as the
court shall deem proper.

     The Registrant's Certificate of Incorporation provides that to the fullest
extent permitted by the Oklahoma General Corporation Act as the same exists or
may hereafter be amended, a director of the Registrant shall not be liable to
the Registrant or its stockholders for monetary damages for breach of fiduciary
duty as a director. The Oklahoma General Corporation Act permits Oklahoma
corporations to include in their certificates of incorporation a provision
eliminating or limiting director liability for monetary damages arising from
breaches of their fiduciary duty. The only limitations imposed under the statute
are that the provision may not eliminate or limit a director's liability (i) for
breaches of the director's duty of loyalty to the corporation or its
stockholders, (ii) for acts or omissions not in good faith or involving
intentional misconduct or known violations of law, (iii) for the payment of
unlawful dividends or unlawful stock purchases or redemptions, or (iv) for
transactions in which the director received an improper personal benefit.

Item 7.   Exemption from Registration Claimed.

          Not applicable.

                                      II-2
<PAGE>

Item 8.   Exhibits.

Exhibit Number                     Description
--------------                     -----------

    4.1             National Environmental Service Co. 1994 Employee Stock Plan
                    (incorporated herein by reference to Exhibit 10.7 to the
                    Registrant's Annual Report on Form 10-KSB for the year ended
                    December 31, 1994 (the "1994 Form 10-KSB")).

    4.2             National Environmental Service Co. 1994 Director Stock
                    Option Plan (incorporated herein by reference to Exhibit
                    10.8 to the 1994 Form 10-KSB).

    5.1*            Opinion of Conner & Winters, A Professional Corporation.

   23.1*            Consent of Tulius Taylor Sartain & Sartain LLP.

   23.2             Consent of Conner & Winters, A Professional Corporation
                    (included in Exhibit 5.1).

   24.1*            Power of Attorney (included on the signature page to this
                    Registration Statement).
_________
    *               Filed herewith.

     The opinion of counsel contemplated by Item 601(b)(5)(i) of Regulation S-K
is being filed only with respect to shares of Common Stock being registered
which may be original issue shares. In lieu of the opinion of counsel or
determination letter contemplated by Item 601(b)(5)(ii) of Regulation S-K, the
Registrant hereby undertakes to submit the National Environmental Service Co.
Employees Savings Trust 401(k) Plan, and any amendment thereto, to the Internal
Revenue Service (the "IRS") in a timely manner, and that it will make all
changes required by the IRS in order to qualify the Employees Savings Trust
401(k) Plan under Section 401 of the Internal Revenue Code.

Item 9.   Undertakings.

     (a)  The undersigned Registrant hereby undertakes:

          (1)  To file, during any period in which offers or sales are being
     made of the securities registered hereby, a post-effective amendment to
     this Registration Statement:

               (i)   To include any prospectus required by Section 10(a)(3) of
          the Securities Act;

                                      II-3
<PAGE>

               (ii)  To reflect in the prospectus any facts or events arising
          after the effective date of this Registration Statement (or the most
          recent post-effective amendment thereof) which, individually or in the
          aggregate, represent a fundamental change in the information set forth
          in this Registration Statement;

               (iii) To include any material information with respect to the
          plan of distribution not previously disclosed in this Registration
          Statement or any material change to such information in this
          Registration Statement;

     provided, however, that the undertakings set forth in paragraphs (a)(1)(i)
     and (a)(1)(ii) above do not apply if the information required to be
     included in a post-effective amendment by those paragraphs is contained in
     periodic reports filed by the registrant pursuant to Section 13 or Section
     15(d) of the Exchange Act that are incorporated by reference in this
     Registration Statement.

          (2)  That, for the purpose of determining any liability under the
     Securities Act, each such post-effective amendment shall be deemed to be a
     new registration statement relating to the securities offered therein, and
     the offering of such securities at that time shall be deemed to be the
     initial bona fide offering thereof.

          (3)  To remove from registration by means of a post-effective
     amendment any of the securities being registered which remain unsold at the
     termination of the offering.

     (b)  The undersigned Registrant hereby further undertakes that, for
purposes of determining any liability under the Securities Act, each filing of
the Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in this Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

     (h)  Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that, in the opinion of the Securities and Exchange
Commission, such indemnification is against public policy as expressed in the
Securities Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
registrant of expenses incurred or paid by a director, officer or controlling
person of the registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.

                                      II-4
<PAGE>

                                  SIGNATURES

     The Registrant. Pursuant to the requirements of the Securities Act of 1933,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Tulsa, State of Oklahoma on the 15/th/ day of
December, 1999.

                                    National Environmental Service Co.


                                    By: /s/ Eddy L. Patterson
                                       ----------------------
                                           Eddy L. Patterson
                                           Chairman and Chief Executive
                                           Officer

     KNOW ALL MEN BY THESE PRESENTS, that each individual whose signature
appears below constitutes and appoints Eddy L. Patterson and Larry G. Johnson,
each of them, his true and lawful attorneys-in-fact and agents with full power
of substitution, for him and in his name, place and stead, in any and all
capacities, to sign any and all amendments (including post-effective amendments)
to this Registration Statement, and to file the same, with all exhibits thereto,
and all documents in connection therewith, with the Securities and Exchange
Commission, granting unto said attorneys-in-fact and agents, full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in and about the premises, as fully to all intents and purposes as he
might or could do in person, hereby ratifying and confirming all that said
attorneys-in-fact and agents, or his or their substitutes, may lawfully do or
cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the dates indicated:


Signature                   Title                          Date
---------                   -----                          ----

/s/ Eddy L. Patterson       Chairman, Chief Executive      December 15, 1999
-------------------------
Eddy L. Patterson           Officer and Director
                            (Principal Executive Officer)


/s/ James Howell            President                      December 15, 1999
-------------------------
James Howell


                                      II-5
<PAGE>

Signature                   Title                         Date
---------                   -----                         ----


/s/ Albert A. McCutchan     Director                      December 20, 1999
--------------------------
Albert A. McCutchan


/s/ Larry G. Johnson        Secretary, Vice President,    December 15, 1999
--------------------------
Larry G. Johnson            Treasurer and Chief
                            Financial Officer


/s/ Robert Watson           Controller                    December 15, 1999
--------------------------
Robert Watson               (Principal Accounting Officer)


/s/ E. R. Foraker           Director                      December 17, 1999
--------------------------
E. R. Foraker


/s/ Dallin Bagley           Director                      December 15, 1999
--------------------------
Dallin Bagley


The Plan. Pursuant to the requirements of the Securities Act of 1933, the
National Environmental Service Co. Employees Savings Trust has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Tulsa, State of Oklahoma on the 15/th/ day of
December, 1999.

                                    National Environmental Service Co.
                                    Employees Savings Trust


                                    By: /s/ Eddy L. Patterson
                                       --------------------------------------
                                       Eddy L. Patterson
                                       Advisory Committee Member

                                      II-6
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 20182}]
{"company-data": {"conformed-name": "NATIONAL ENVIRONMENTAL SERVICE CO", "cik": "0000922868", "assigned-sic": "4955", "irs-number": "731296420", "state-of-incorporation": "OK", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-93113", "film-number": "99777648"}, "business-address": {"street1": "12331 EAST 60TH ST", "city": "TULSA", "state": "OK", "zip": "74146", "phone": "9182502227"}, "mail-address": {"street1": "12331 EAST 60TH ST", "city": "TULSA", "state": "OK", "zip": "74146"}}
As filed with the Securities and Exchange Commission on December 20, 1999.
                                             Registration No.333-
--------------------------------------------------------------------------------

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549
                                   --------

                                   FORM S-8
            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                                   --------

                      NATIONAL ENVIRONMENTAL SERVICE CO.
            (Exact name of registrant as specified in its charter)

           Oklahoma                                        73-1296420
(State or other jurisdiction of                        (I.R.S. employer
incorporation or organization)                         identification no.)

                             12331 East 60th Street
                             Tulsa, Oklahoma  74146
          (Address of principal executive offices including zip code)

          National Environmental Service Co. 1994 Employee Stock Plan
      National Environmental Service Co. 1994 Director Stock Option Plan
    National Environmental Service Co. Employees Savings Trust 401(k) Plan
                           (Full title of the plan)
                                   --------

                               Larry G. Johnson
                            12331 East 60th Street
                            Tulsa, Oklahoma  74146
                    (Name and address of agent for service)

 Telephone number, including area code, of agent for service:  (918) 250-2227

                        CALCULATION OF REGISTRATION FEE
------------------------------------------------------------------------------------------------------------------
                                                              Proposed         Proposed
                                                              maximum           maximum         Amount of
Title of securities                       Amount to be     offering price      aggregate     registration fee
to be registered                          registered(1)       per share     offering price
------------------------------------------------------------------------------------------------------------------
1994 Employee Stock Plan
Common Stock, $.01 par value
(Outstanding options)                   257,000 shares          $2.494 (2)   $  641,000 (2)
------------------------------------------------------------------------------------------------------------------
1994 Employee Stock Plan
Common Stock, $.01 par value
(Options available for future grant)    516,735 shares          $2.875 (3)   $1,485,613 (3)
------------------------------------------------------------------------------------------------------------------
1994 Director Stock Option Plan
Common Stock, $.01 par value
(Options available for future grant)    150,000 shares          $2.875 (3)   $  431,250 (3)
------------------------------------------------------------------------------------------------------------------
Employees Savings Trust 401(k)
Common Stock, $.01 par value            120,000 shares          $2.875 (3)   $  345,000 (3)
------------------------------------------------------------------------------------------------------------------
Total Registration Fee                                                       $2,902,863       $  767.00
==================================================================================================================
(1) In addition, pursuant to Rule 416(c) under the Securities Act of 1933, this
Registration Statement also covers an indeterminate amount of interests to be
offered or sold pursuant to the Employees Savings Trust 401(k).

(2) The computation is based upon the weighted average exercise price per share
of $2.494 as to outstanding options to purchase 257,000 shares under the 1994
Employee Stock Plan.

(3) Estimated solely for the purposes of calculating the registration fee
pursuant to Rule 457(h), on the basis of the average of the bid and ask price
for the Common Stock as reported on the Nasdaq SmallCap Market on December 14,
1999.
PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

Information required by Part I of Form S-8 to be contained in the Section 10(a)
Prospectus is omitted from this Registration Statement in accordance with Rule
428 under the Securities Act of 1933, as amended (the "Securities Act"), and the
Note to Part I of Form S-8.
PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.   Incorporation of Documents by Reference.

     The following documents and information previously filed by the Registrant
with the Securities and Exchange Commission are incorporated by reference in
this Registration Statement:

     (1)  The Registrant's Annual Report on Form 10-KSB for the year ended
          December 31, 1998, as amended by Amendment No. 1 on Form 10-KSB/A
          filed with the Commission on October 8, 1999;

     (2)  The Registrant's Quarterly Reports on Form 10-QSB for the quarters
          ended March 31, 1999, June 30, 1999 and September 30, 1999;

     (3)  The Registrant's Current Report on Form 8-K filed with the Commission
          on May 21, 1999, as amended by Amendment No. 1 on Form 8-K/A filed
          with the Commission on July 21, 1999;

     (4)  The Registrant's Current Report on Form 8-K filed with the Commission
          on September 22, 1999, as amended by Amendment No. 1 on Form 8-K/A
          filed with the Commission on November 12, 1999; and

     (5)  The description of the Registrant's Common Stock contained in the
          Registration Statement on Form 8-A declared effective by the
          Commission on September 13, 1994, and including any amendment or
          report heretofore or hereafter filed for the purpose of updating the
          description of the Registrant's Common Stock contained therein.

     In addition, all documents subsequently filed by the Registrant or the
Employees Savings Trust 401(k) Plan pursuant to Sections 13(a), 13(c), 14 and
15(d) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"),
prior to the filing of a post-effective amendment which indicates that all
securities offered hereby have been sold or which deregisters all securities
offered hereby then remaining unsold, shall be deemed to be incorporated by
reference in this Registration Statement and to be a part hereof from their
respective dates of filing. Any statement contained in a document incorporated
by reference shall be deemed to be modified or superseded for purposes of this
Registration Statement to the extent that a statement contained in any other
subsequently filed incorporated document modifies or supersedes such statement.
Any such statement so modified or superseded shall not be deemed, except as so
modified or superseded, to constitute a part of this Registration Statement.

Item 4.   Description of Securities.

          Not applicable.

                                      II-1
Item 5.   Interests of Named Experts and Counsel.

          Not applicable.

Item 6.   Indemnification of Directors and Officers.

     The Registrant's By-Laws provide that each person who was or is made a
party to, or is involved in, any action, suit or proceeding by reason of the
fact that he or she was a director or officer of the Registrant (or was serving
at the request of the Registrant as a director, officer, employee or agent for
another entity) will be indemnified and held harmless by the Registrant, to the
full extent authorized by the Oklahoma General Corporation Act.

     Under Section 1031 of the Oklahoma General Corporation Act, a corporation
may indemnify a director, officer, employee or agent of the corporation against
expenses (including attorneys' fees), judgments, fines and amounts paid in
settlement actually and reasonably incurred by him or her if he or she acted in
good faith and in a manner he or she reasonably believed to be in or not opposed
to the best interests of the corporation and, with respect to any criminal
action or proceeding, had no reasonable cause to believe his or her conduct was
unlawful. In the case of an action brought by or in the right of a corporation,
the corporation may indemnify a director, officer, employee or agent of the
corporation against expenses (including attorneys' fees) actually and reasonably
incurred by him or her if he or she acted in good faith and in a manner he or
she reasonably believed to be in the best interests of the corporation, except
that no indemnification shall be made in respect of any claim, issue or matter
as to which such person shall have been adjudged to be liable to the corporation
unless a court finds that, in view of all the circumstances of the case, such
person is fairly and reasonably entitled to indemnity for such expenses as the
court shall deem proper.

     The Registrant's Certificate of Incorporation provides that to the fullest
extent permitted by the Oklahoma General Corporation Act as the same exists or
may hereafter be amended, a director of the Registrant shall not be liable to
the Registrant or its stockholders for monetary damages for breach of fiduciary
duty as a director. The Oklahoma General Corporation Act permits Oklahoma
corporations to include in their certificates of incorporation a provision
eliminating or limiting director liability for monetary damages arising from
breaches of their fiduciary duty. The only limitations imposed under the statute
are that the provision may not eliminate or limit a director's liability (i) for
breaches of the director's duty of loyalty to the corporation or its
stockholders, (ii) for acts or omissions not in good faith or involving
intentional misconduct or known violations of law, (iii) for the payment of
unlawful dividends or unlawful stock purchases or redemptions, or (iv) for
transactions in which the director received an improper personal benefit.

Item 7.   Exemption from Registration Claimed.

          Not applicable.

                                      II-2
Item 8.   Exhibits.

Exhibit Number                     Description
--------------                     -----------

    4.1             National Environmental Service Co. 1994 Employee Stock Plan
                    (incorporated herein by reference to Exhibit 10.7 to the
                    Registrant's Annual Report on Form 10-KSB for the year ended
                    December 31, 1994 (the "1994 Form 10-KSB")).

    4.2             National Environmental Service Co. 1994 Director Stock
                    Option Plan (incorporated herein by reference to Exhibit
                    10.8 to the 1994 Form 10-KSB).

    5.1*            Opinion of Conner & Winters, A Professional Corporation.

   23.1*            Consent of Tulius Taylor Sartain & Sartain LLP.

   23.2             Consent of Conner & Winters, A Professional Corporation
                    (included in Exhibit 5.1).

   24.1*            Power of Attorney (included on the signature page to this
                    Registration Statement).
_________
    *               Filed herewith.

     The opinion of counsel contemplated by Item 601(b)(5)(i) of Regulation S-K
is being filed only with respect to shares of Common Stock being registered
which may be original issue shares. In lieu of the opinion of counsel or
determination letter contemplated by Item 601(b)(5)(ii) of Regulation S-K, the
Registrant hereby undertakes to submit the National Environmental Service Co.
Employees Savings Trust 401(k) Plan, and any amendment thereto, to the Internal
Revenue Service (the "IRS") in a timely manner, and that it will make all
changes required by the IRS in order to qualify the Employees Savings Trust
401(k) Plan under Section 401 of the Internal Revenue Code.

Item 9.   Undertakings.

     (a)  The undersigned Registrant hereby undertakes:

          (1)  To file, during any period in which offers or sales are being
     made of the securities registered hereby, a post-effective amendment to
     this Registration Statement:

               (i)   To include any prospectus required by Section 10(a)(3) of
          the Securities Act;

                                      II-3
(ii)  To reflect in the prospectus any facts or events arising
          after the effective date of this Registration Statement (or the most
          recent post-effective amendment thereof) which, individually or in the
          aggregate, represent a fundamental change in the information set forth
          in this Registration Statement;

               (iii) To include any material information with respect to the
          plan of distribution not previously disclosed in this Registration
          Statement or any material change to such information in this
          Registration Statement;

     provided, however, that the undertakings set forth in paragraphs (a)(1)(i)
     and (a)(1)(ii) above do not apply if the information required to be
     included in a post-effective amendment by those paragraphs is contained in
     periodic reports filed by the registrant pursuant to Section 13 or Section
     15(d) of the Exchange Act that are incorporated by reference in this
     Registration Statement.

          (2)  That, for the purpose of determining any liability under the
     Securities Act, each such post-effective amendment shall be deemed to be a
     new registration statement relating to the securities offered therein, and
     the offering of such securities at that time shall be deemed to be the
     initial bona fide offering thereof.

          (3)  To remove from registration by means of a post-effective
     amendment any of the securities being registered which remain unsold at the
     termination of the offering.

     (b)  The undersigned Registrant hereby further undertakes that, for
purposes of determining any liability under the Securities Act, each filing of
the Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in this Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

     (h)  Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that, in the opinion of the Securities and Exchange
Commission, such indemnification is against public policy as expressed in the
Securities Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
registrant of expenses incurred or paid by a director, officer or controlling
person of the registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.

                                      II-4
SIGNATURES

     The Registrant. Pursuant to the requirements of the Securities Act of 1933,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Tulsa, State of Oklahoma on the 15/th/ day of
December, 1999.

                                    National Environmental Service Co.

                                    By: /s/ Eddy L. Patterson
                                       ----------------------
                                           Eddy L. Patterson
                                           Chairman and Chief Executive
                                           Officer

     KNOW ALL MEN BY THESE PRESENTS, that each individual whose signature
appears below constitutes and appoints Eddy L. Patterson and Larry G. Johnson,
each of them, his true and lawful attorneys-in-fact and agents with full power
of substitution, for him and in his name, place and stead, in any and all
capacities, to sign any and all amendments (including post-effective amendments)
to this Registration Statement, and to file the same, with all exhibits thereto,
and all documents in connection therewith, with the Securities and Exchange
Commission, granting unto said attorneys-in-fact and agents, full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in and about the premises, as fully to all intents and purposes as he
might or could do in person, hereby ratifying and confirming all that said
attorneys-in-fact and agents, or his or their substitutes, may lawfully do or
cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the dates indicated:

Signature                   Title                          Date
---------                   -----                          ----

/s/ Eddy L. Patterson       Chairman, Chief Executive      December 15, 1999
-------------------------
Eddy L. Patterson           Officer and Director
                            (Principal Executive Officer)

/s/ James Howell            President                      December 15, 1999
-------------------------
James Howell

                                      II-5
Signature                   Title                         Date
---------                   -----                         ----

/s/ Albert A. McCutchan     Director                      December 20, 1999
--------------------------
Albert A. McCutchan

/s/ Larry G. Johnson        Secretary, Vice President,    December 15, 1999
--------------------------
Larry G. Johnson            Treasurer and Chief
                            Financial Officer

/s/ Robert Watson           Controller                    December 15, 1999
--------------------------
Robert Watson               (Principal Accounting Officer)

/s/ E. R. Foraker           Director                      December 17, 1999
--------------------------
E. R. Foraker

/s/ Dallin Bagley           Director                      December 15, 1999
--------------------------
Dallin Bagley

The Plan. Pursuant to the requirements of the Securities Act of 1933, the
National Environmental Service Co. Employees Savings Trust has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Tulsa, State of Oklahoma on the 15/th/ day of
December, 1999.

                                    National Environmental Service Co.
                                    Employees Savings Trust

                                    By: /s/ Eddy L. Patterson
                                       --------------------------------------
                                       Eddy L. Patterson
                                       Advisory Committee Member

                                      II-6