<PAGE>   1
      AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JULY 2, 1999

                                                    Registration No. 333-
                                                                         -------
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                -----------------

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

                                -----------------

                                   ENRON CORP.
             (Exact name of registrant as specified in its charter)

           OREGON                                       47-0255140
(State or other jurisdiction of                      (I.R.S. Employer
incorporation or organization)                      Identification No.)

                                1400 SMITH STREET
                              HOUSTON, TEXAS 77002
          (Address of principal executive offices, including zip code)

                                -----------------

                AMENDED AND RESTATED ENRON CORP. 1991 STOCK PLAN
                            (Full title of the plan)

                                  Rex R. Rogers
                  Vice President and Associate General Counsel
                                   Enron Corp.
                                1400 Smith Street
                              Houston, Texas 77002
                     (Name and address of agent for service)

                                 (713) 853-3069
          (Telephone number, including area code, of agent for service)



                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
====================================================================================================================
          Title of                   Amount         Proposed maximum       Proposed maximum
      securities to be                to be          offering price            aggregate             Amount of
         registered                registered         per share(1)         offering price(1)     registration fee
====================================================================================================================
<S>                             <C>              <C>                    <C>                    <C>
Common Stock,
no par value                      10,000,000             $77.125             $771,250,000            $214,408
                                  Shares (2)

====================================================================================================================
</TABLE>

(1)  Estimated solely for purpose of calculating the registration fee (based
     upon the average of the high and low prices of the Common Stock on the New
     York Stock Exchange composite transactions reporting system on June 25,
     1999.

(2)  This Registration Statement shall also include any additional shares of
     Common Stock issuable pursuant to the antidilution provisions of the Plan.

This registration statement is being filed, in accordance with General
Instruction E to Form S-8, to register additional shares of Common Stock for
sale under the Amended and Restated Enron Corp. 1991 Stock Plan. The contents of
the registrant's Form S-8 Registration Statement (No. 33-52768) relating to the
same employee benefit plan are incorporated by reference in this registration
statement.


<PAGE>   2


                     INFORMATION NOT REQUIRED IN PROSPECTUS

         The following documents are filed as part of this registration
statement, in accordance with General Instruction E to Form S-8:

<TABLE>
<CAPTION>
EXHIBITS.
---------
<S>    <C>
*3.1 - Amended and Restated Articles of Incorporation of Enron Corp. (Annex E to
       the Proxy Statement/Prospectus included in Enron Corp.'s Registration
       Statement on Form S-4 - File No. 333-13791).

*3.2 - Articles of Merger of Enron Oregon Corp., an Oregon corporation, and
       Enron Corp., a Delaware corporation (Exhibit 3.02 to Post-Effective
       Amendment No. 1 to Enron Corp.'s Registration Statement on Form S-3 -
       File No. 33-60417).

*3.3 - Articles of Merger of Enron Corp., an Oregon corporation, and Portland
       General Corporation, an Oregon corporation (Exhibit 3.03 to
       Post-Effective Amendment No. 1 to Enron Corp.'s Registration Statement on
       Form S-3 - File No. 33-60417).

*3.4 - Bylaws of Enron Corp. (Exhibit 3.04 to Post-Effective Amendment No. 1 to
       Enron Corp.'s Registration Statement on Form S-3 - File No. 33-60417).

*3.5 - Form of Series Designation for the Enron Convertible Preferred Stock
       (Annex F to the Proxy Statement/Prospectus included in Enron's
       Registration Statement on Form S-4 File No. 333-13791).

*3.6 - Form of Series Designation for the Enron 9.142% Preferred Stock (Annex G
       to the Proxy Statement/Prospectus included in Enron's Registration
       Statement on Form S-4 - File No. 333-13791).

*3.7 - Form of Series Designation for the Enron Series A Junior Voting
       Convertible Preferred Stock (Exhibit 3.07 to Enron's Registration
       Statement on Form S-3 - File No. 333-44133).

*3.8 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series A (Exhibit 4.01 to Enron's Form 8-K filed on January 26, 1999).

*3.9 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series B (Exhibit 4.02 to Enron's Form 8-K filed on January 26, 1999).

*4   - Enron Corp. 1991 Stock Plan, as amended and restated (Exhibit B, Enron
       Corp. Proxy Statement for 1999 Annual Meeting of Shareholders).

5    - Opinion of James V. Derrick, Jr., Esq., Senior Vice President and General
       Counsel of Enron Corp.

23.1 - Consent of Arthur Andersen LLP.

23.2 - Consent of DeGolyer and MacNaughton.

23.3 - The consent of James V. Derrick, Jr., Esq., is contained in his opinion
       filed as Exhibit 5 hereto.

24   - Powers of Attorney of certain directors of Enron Corp.
</TABLE>

------------------------------
*  Incorporated by reference as indicated.


<PAGE>   3


                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
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 or amendment to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Houston, State of Texas,
on the 1st day of July, 1999.

                                           ENRON CORP.


                                           By: /s/ RICHARD A. CAUSEY
                                              ----------------------------------
                                              Richard A. Causey
                                              Senior Vice President and Chief
                                                 Accounting, Information and
                                                 Administrative Officer

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this registration statement or amendment has been signed by the following
persons in the capacities indicated and on the 1st day of July, 1999.

<TABLE>
<CAPTION>
                  Signature                                      Title
                  ---------                                      -----
<S>                                        <C>
             /s/ KENNETH L. LAY                         Chairman of the Board,
        -----------------------------            Chief Executive Officer and Director
               Kenneth L. Lay                        (Principal Executive Officer)



           /s/ RICHARD A. CAUSEY                       Senior Vice President and
        -----------------------------              Chief Accounting, Information and
              Richard A. Causey                         Administrative Officer
                                                    (Principal Accounting Officer)


           /s/ ANDREW S. FASTOW            Senior Vice President and Chief Financial Officer
        -----------------------------                (Principal Financial Officer)
              Andrew S. Fastow



             ROBERT A. BELFER *                                Director
        -----------------------------
              Robert A. Belfer


            NORMAN P. BLAKE, JR. *                             Director
        -----------------------------
            Norman P. Blake, Jr.


               RONNIE C. CHAN *                                Director
        -----------------------------
               Ronnie C. Chan


              JOHN H. DUNCAN *                                 Director
        -----------------------------
               John H. Duncan


                JOE H. FOY *                                   Director
        -----------------------------
                 Joe H. Foy


              WENDY L. GRAMM *                                 Director
        -----------------------------
               Wendy L. Gramm
</TABLE>


<PAGE>   4


<TABLE>
<S>                                        <C>
              KEN L. HARRISON*                                 Director
        -----------------------------
               Ken L. Harrison


            ROBERT K. JAEDICKE *                               Director
        -----------------------------
             Robert K. Jaedicke


           CHARLES A. LeMAISTRE *                              Director
        -----------------------------
            Charles A. LeMaistre


              JOHN MENDELSOHN *                                Director
        -----------------------------
               John Mendelsohn


              JEROME J. MEYER*                                 Director
        -----------------------------
               Jerome J. Meyer


            JEFFREY K. SKILLING *                       Director, President and
        -----------------------------                   Chief Operating Officer
             Jeffrey K. Skilling


               JOHN WAKEHAM *                                  Director
        -----------------------------
                John Wakeham


          HERBERT S. WINOKUR, JR. *                            Director
        -----------------------------
           Herbert S. Winokur, Jr.
</TABLE>



*By:   /s/ REBECCA C. CARTER
    -----------------------------
           Rebecca C. Carter
            Attorney-in-Fact


<PAGE>   5



                                  EXHIBIT INDEX


<TABLE>
<CAPTION>
EXHIBITS                 DESCRIPTION OF EXHIBIT
--------                 ----------------------
<S>    <C>
*3.1 - Amended and Restated Articles of Incorporation of Enron Corp. (Annex E to
       the Proxy Statement/Prospectus included in Enron Corp.'s Registration
       Statement on Form S-4 - File No. 333-13791).

*3.2 - Articles of Merger of Enron Oregon Corp., an Oregon corporation, and
       Enron Corp., a Delaware corporation (Exhibit 3.02 to Post-Effective
       Amendment No. 1 to Enron Corp.'s Registration Statement on Form S-3 -
       File No. 33-60417).

*3.3 - Articles of Merger of Enron Corp., an Oregon corporation, and Portland
       General Corporation, an Oregon corporation (Exhibit 3.03 to
       Post-Effective Amendment No. 1 to Enron Corp.'s Registration Statement on
       Form S-3 - File No. 33-60417).

*3.4 - Bylaws of Enron Corp. (Exhibit 3.04 to Post-Effective Amendment No. 1 to
       Enron Corp.'s Registration Statement on Form S-3 - File No. 33-60417).

*3.5 - Form of Series Designation for the Enron Convertible Preferred Stock
       (Annex F to the Proxy Statement/Prospectus included in Enron's
       Registration Statement on Form S-4 File No. 333-13791).

*3.6 - Form of Series Designation for the Enron 9.142% Preferred Stock (Annex G
       to the Proxy Statement/Prospectus included in Enron's Registration
       Statement on Form S-4 - File No. 333-13791).

*3.7 - Form of Series Designation for the Enron Series A Junior Voting
       Convertible Preferred Stock (Exhibit 3.07 to Enron's Registration
       Statement on Form S-3 - File No. 333-44133).

*3.8 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series A (Exhibit 4.01 to Enron's Form 8-K filed on January 26, 1999).

*3.9 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series B (Exhibit 4.02 to Enron's Form 8-K filed on January 26, 1999).

*4   - Enron Corp. 1991 Stock Plan, as amended and restated (Exhibit B, Enron
       Corp. Proxy Statement for 1999 Annual Meeting of Shareholders).

5    - Opinion of James V. Derrick, Jr., Esq., Senior Vice President and General
       Counsel of Enron Corp.

23.1 - Consent of Arthur Andersen LLP.

23.2 - Consent of DeGolyer and MacNaughton.

23.3 - The consent of James V. Derrick, Jr., Esq., is contained in his opinion
       filed as Exhibit 5 hereto.

24   - Powers of Attorney of certain directors of Enron Corp.
</TABLE>

------------------------------
*  Incorporated by reference as indicated.
[{"type": "S-8", "sequence": "1", "description": "ENRON CORP. - 1991 STOCK PLAN", "secsgml_size_bytes": 13730}]
{"company-data": {"conformed-name": "ENRON CORP/OR/", "cik": "0001024401", "assigned-sic": "5172", "irs-number": "470255140", "state-of-incorporation": "OR", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-82227", "film-number": "99658951"}, "business-address": {"street1": "1400 SMITH ST", "city": "HOUSTON", "state": "TX", "zip": "77002-7369", "phone": "7138536161"}, "mail-address": {"street1": "1400 SMITH ST", "city": "HOUSTON", "state": "TX", "zip": "75002-7369"}, "former-company": {"former-conformed-name": "ENRON OREGON CORP", "date-changed": "19961008"}}
1
      AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JULY 2, 1999

                                                    Registration No. 333-
                                                                         -------
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                -----------------

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

                                -----------------

                                   ENRON CORP.
             (Exact name of registrant as specified in its charter)

           OREGON                                       47-0255140
(State or other jurisdiction of                      (I.R.S. Employer
incorporation or organization)                      Identification No.)

                                1400 SMITH STREET
                              HOUSTON, TEXAS 77002
          (Address of principal executive offices, including zip code)

                                -----------------

                AMENDED AND RESTATED ENRON CORP. 1991 STOCK PLAN
                            (Full title of the plan)

                                  Rex R. Rogers
                  Vice President and Associate General Counsel
                                   Enron Corp.
                                1400 Smith Street
                              Houston, Texas 77002
                     (Name and address of agent for service)

                                 (713) 853-3069
          (Telephone number, including area code, of agent for service)

                        CALCULATION OF REGISTRATION FEE
====================================================================================================================
          Title of                   Amount         Proposed maximum       Proposed maximum
      securities to be                to be          offering price            aggregate             Amount of
         registered                registered         per share(1)         offering price(1)     registration fee
====================================================================================================================
Common Stock,
no par value                      10,000,000             $77.125             $771,250,000            $214,408
                                  Shares (2)

====================================================================================================================
(1)  Estimated solely for purpose of calculating the registration fee (based
     upon the average of the high and low prices of the Common Stock on the New
     York Stock Exchange composite transactions reporting system on June 25,
     1999.

(2)  This Registration Statement shall also include any additional shares of
     Common Stock issuable pursuant to the antidilution provisions of the Plan.

This registration statement is being filed, in accordance with General
Instruction E to Form S-8, to register additional shares of Common Stock for
sale under the Amended and Restated Enron Corp. 1991 Stock Plan. The contents of
the registrant's Form S-8 Registration Statement (No. 33-52768) relating to the
same employee benefit plan are incorporated by reference in this registration
statement.
2

                     INFORMATION NOT REQUIRED IN PROSPECTUS

         The following documents are filed as part of this registration
statement, in accordance with General Instruction E to Form S-8:
EXHIBITS.
---------
*3.1 - Amended and Restated Articles of Incorporation of Enron Corp. (Annex E to
       the Proxy Statement/Prospectus included in Enron Corp.'s Registration
       Statement on Form S-4 - File No. 333-13791).

*3.2 - Articles of Merger of Enron Oregon Corp., an Oregon corporation, and
       Enron Corp., a Delaware corporation (Exhibit 3.02 to Post-Effective
       Amendment No. 1 to Enron Corp.'s Registration Statement on Form S-3 -
       File No. 33-60417).

*3.3 - Articles of Merger of Enron Corp., an Oregon corporation, and Portland
       General Corporation, an Oregon corporation (Exhibit 3.03 to
       Post-Effective Amendment No. 1 to Enron Corp.'s Registration Statement on
       Form S-3 - File No. 33-60417).

*3.4 - Bylaws of Enron Corp. (Exhibit 3.04 to Post-Effective Amendment No. 1 to
       Enron Corp.'s Registration Statement on Form S-3 - File No. 33-60417).

*3.5 - Form of Series Designation for the Enron Convertible Preferred Stock
       (Annex F to the Proxy Statement/Prospectus included in Enron's
       Registration Statement on Form S-4 File No. 333-13791).

*3.6 - Form of Series Designation for the Enron 9.142% Preferred Stock (Annex G
       to the Proxy Statement/Prospectus included in Enron's Registration
       Statement on Form S-4 - File No. 333-13791).

*3.7 - Form of Series Designation for the Enron Series A Junior Voting
       Convertible Preferred Stock (Exhibit 3.07 to Enron's Registration
       Statement on Form S-3 - File No. 333-44133).

*3.8 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series A (Exhibit 4.01 to Enron's Form 8-K filed on January 26, 1999).

*3.9 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series B (Exhibit 4.02 to Enron's Form 8-K filed on January 26, 1999).

*4   - Enron Corp. 1991 Stock Plan, as amended and restated (Exhibit B, Enron
       Corp. Proxy Statement for 1999 Annual Meeting of Shareholders).

5    - Opinion of James V. Derrick, Jr., Esq., Senior Vice President and General
       Counsel of Enron Corp.

23.1 - Consent of Arthur Andersen LLP.

23.2 - Consent of DeGolyer and MacNaughton.

23.3 - The consent of James V. Derrick, Jr., Esq., is contained in his opinion
       filed as Exhibit 5 hereto.

24   - Powers of Attorney of certain directors of Enron Corp.
------------------------------
*  Incorporated by reference as indicated.
3

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
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 or amendment to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Houston, State of Texas,
on the 1st day of July, 1999.

                                           ENRON CORP.

                                           By: /s/ RICHARD A. CAUSEY
                                              ----------------------------------
                                              Richard A. Causey
                                              Senior Vice President and Chief
                                                 Accounting, Information and
                                                 Administrative Officer

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this registration statement or amendment has been signed by the following
persons in the capacities indicated and on the 1st day of July, 1999.
Signature                                      Title
                  ---------                                      -----
/s/ KENNETH L. LAY                         Chairman of the Board,
        -----------------------------            Chief Executive Officer and Director
               Kenneth L. Lay                        (Principal Executive Officer)

           /s/ RICHARD A. CAUSEY                       Senior Vice President and
        -----------------------------              Chief Accounting, Information and
              Richard A. Causey                         Administrative Officer
                                                    (Principal Accounting Officer)

           /s/ ANDREW S. FASTOW            Senior Vice President and Chief Financial Officer
        -----------------------------                (Principal Financial Officer)
              Andrew S. Fastow

             ROBERT A. BELFER *                                Director
        -----------------------------
              Robert A. Belfer

            NORMAN P. BLAKE, JR. *                             Director
        -----------------------------
            Norman P. Blake, Jr.

               RONNIE C. CHAN *                                Director
        -----------------------------
               Ronnie C. Chan

              JOHN H. DUNCAN *                                 Director
        -----------------------------
               John H. Duncan

                JOE H. FOY *                                   Director
        -----------------------------
                 Joe H. Foy

              WENDY L. GRAMM *                                 Director
        -----------------------------
               Wendy L. Gramm
4
KEN L. HARRISON*                                 Director
        -----------------------------
               Ken L. Harrison

            ROBERT K. JAEDICKE *                               Director
        -----------------------------
             Robert K. Jaedicke

           CHARLES A. LeMAISTRE *                              Director
        -----------------------------
            Charles A. LeMaistre

              JOHN MENDELSOHN *                                Director
        -----------------------------
               John Mendelsohn

              JEROME J. MEYER*                                 Director
        -----------------------------
               Jerome J. Meyer

            JEFFREY K. SKILLING *                       Director, President and
        -----------------------------                   Chief Operating Officer
             Jeffrey K. Skilling

               JOHN WAKEHAM *                                  Director
        -----------------------------
                John Wakeham

          HERBERT S. WINOKUR, JR. *                            Director
        -----------------------------
           Herbert S. Winokur, Jr.
*By:   /s/ REBECCA C. CARTER
    -----------------------------
           Rebecca C. Carter
            Attorney-in-Fact
5

                                  EXHIBIT INDEX
EXHIBITS                 DESCRIPTION OF EXHIBIT
--------                 ----------------------
*3.1 - Amended and Restated Articles of Incorporation of Enron Corp. (Annex E to
       the Proxy Statement/Prospectus included in Enron Corp.'s Registration
       Statement on Form S-4 - File No. 333-13791).

*3.2 - Articles of Merger of Enron Oregon Corp., an Oregon corporation, and
       Enron Corp., a Delaware corporation (Exhibit 3.02 to Post-Effective
       Amendment No. 1 to Enron Corp.'s Registration Statement on Form S-3 -
       File No. 33-60417).

*3.3 - Articles of Merger of Enron Corp., an Oregon corporation, and Portland
       General Corporation, an Oregon corporation (Exhibit 3.03 to
       Post-Effective Amendment No. 1 to Enron Corp.'s Registration Statement on
       Form S-3 - File No. 33-60417).

*3.4 - Bylaws of Enron Corp. (Exhibit 3.04 to Post-Effective Amendment No. 1 to
       Enron Corp.'s Registration Statement on Form S-3 - File No. 33-60417).

*3.5 - Form of Series Designation for the Enron Convertible Preferred Stock
       (Annex F to the Proxy Statement/Prospectus included in Enron's
       Registration Statement on Form S-4 File No. 333-13791).

*3.6 - Form of Series Designation for the Enron 9.142% Preferred Stock (Annex G
       to the Proxy Statement/Prospectus included in Enron's Registration
       Statement on Form S-4 - File No. 333-13791).

*3.7 - Form of Series Designation for the Enron Series A Junior Voting
       Convertible Preferred Stock (Exhibit 3.07 to Enron's Registration
       Statement on Form S-3 - File No. 333-44133).

*3.8 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series A (Exhibit 4.01 to Enron's Form 8-K filed on January 26, 1999).

*3.9 - Statement of Resolutions Establishing A Series of Preferred Stock of
       Enron Corp. - Mandatorily Convertible Single Reset Preferred Stock,
       Series B (Exhibit 4.02 to Enron's Form 8-K filed on January 26, 1999).

*4   - Enron Corp. 1991 Stock Plan, as amended and restated (Exhibit B, Enron
       Corp. Proxy Statement for 1999 Annual Meeting of Shareholders).

5    - Opinion of James V. Derrick, Jr., Esq., Senior Vice President and General
       Counsel of Enron Corp.

23.1 - Consent of Arthur Andersen LLP.

23.2 - Consent of DeGolyer and MacNaughton.

23.3 - The consent of James V. Derrick, Jr., Esq., is contained in his opinion
       filed as Exhibit 5 hereto.

24   - Powers of Attorney of certain directors of Enron Corp.
------------------------------
*  Incorporated by reference as indicated.