Document:

<PAGE>

                                                                   EXHIBIT 10.22

                  AMENDMENT TO SECURITIES PURCHASE AGREEMENT

          This Amendment to Securities Purchase Agreement (the "Amendment")
dated as of November ___, 1999, is entered into by and between MIDDLE BAY OIL
COMPANY, INC., an Alabama corporation ("Corporation") and 3TEC Energy Company
L.L.C., a Delaware limited liability company f/k/a 3TEC Energy Corporation
("3TEC").

                                   RECITALS

     WHEREAS, on July 1, 1999, the Corporation and 3TEC entered into a certain
Securities Purchase Agreement (the "Agreement"); and

     WHEREAS, the parties hereto wish to amend the Agreement.

     NOW, THEREFORE, in consideration of the mutual promises contained herein
and other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the parties hereto agree as follows:

     1.   All references to "Compass Senior Credit Agreement", "Compass Senior
Debt", and "Compass Senior Debt Documents" in the Agreement and all related
documents (including the Note and Warrants) are hereby replaced with the terms
"Senior Credit Agreement", "Senior Debt", and "Senior Debt Documents"
respectively.

     2.   Section 1.1 is hereby amended to include the following terms:

          "Senior Credit Agreement" means that certain Restated Credit Agreement
dated November ___, 1999, by and among Middle Bay Oil Company, Inc., Enex
Resources Corporation and Middle Bay Production Company, Inc., as borrowers, and
Bank One, Texas, N.A., as agent and a lender, and each other lender or agent now
or hereafter a party thereto and their successors and assigns, and any
replacements, refinancings, amendments, renewals or extensions thereof, whether
with the existing agent and lenders or other agents and lenders."

          "Senior Debt" means all Debt of the Company or any of its Subsidiaries
outstanding under the Senior Debt Documents, including all renewals, extensions,
increases, refinancings, restatements and replacements thereof."

          "Senior Debt Documents" means the Senior Credit Agreement and all
promissory notes, security agreements, mortgages, deeds of trust, assignments,
guaranties and other documents, instruments and agreements executed and
delivered pursuant to the Senior Credit Agreement evidencing, securing,
guaranteeing or otherwise pertaining to the Senior Debt and all other

                                       1
<PAGE>

obligations arising under the Senior Credit Agreement, as the foregoing may be
amended, renewed, extended, supplemented, increased or otherwise modified from
time to time."

     3.   The following definition in Section 1.1 is hereby deleted in its
entirety and replaced with the following:

          "Senior Lender" means any holder of any Senior Debt."

     4.   Section 9.10 (b) is hereby deleted in its entirety and replaced with
the following:

     "(b) The Company will not, nor will it permit any of its Subsidiaries to,
enter into any amendment or modification of its Charter Documents or waive or
fail to enforce any material right of the Company or any of its Subsidiaries
thereunder."

     5.   Exhibit H.  Exhibit H of the Agreement is hereby deleted in its
          ----------
entirety and replaced with Exhibit H attached hereto.

     6.   Terms Defined in Agreement.  As used herein, each term defined in the
          ---------------------------
Agreement shall have the meaning assigned thereto in the Agreement, unless
expressly provided herein to the contrary.

     7.   Full Force and Effect.  Except with respect to the changes made in
          ----------------------
this Amendment, the terms and provisions of the Agreement are in full force and
effect.

     8.   Notices.  Any notice to be given by any party hereunder to any other
          --------
shall be in writing, mailed by certified or registered mail, return receipt
requested, and shall be addressed to the other parties at the addresses listed
on the signature pages hereof.  All such notices shall be deemed to be given
three (3) days after the date of mailing thereof.

     9.   Binding Effect.  This Amendment shall be binding upon the parties
          ---------------
hereto and their respective successors, personal representatives and permitted
assigns.

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first above written.

"CORPORATION"

MIDDLE BAY OIL COMPANY, INC.

By:
   -----------------------------
Name: Floyd C. Wilson
Title: President and Chief Executive Officer

                                       2
<PAGE>

Address for Notice:

Middle Bay Oil Company, Inc.
1221 Lamar Street, Suite 1020
Houston, TX 77010
Fax: (713) 650-0352

"3TEC"

3TEC ENERGY COMPANY L.L.C

By:__________________________
Name: Floyd C. Wilson
Title: Managing Director

Address for Notice:

3TEC Energy Company L.L.C.
5910 N. Central Expressway
Suite 1150
Dallas, TX 75206
Fax: (214) 373-9731

                                       3
<PAGE>

                                    EXHIBIT H
                      OTHER SECURITIES PURCHASE AGREEMENTS

     Securities Purchase Agreement by and between Shoemaker Family Partners, LP
and Middle Bay Oil Company, Inc., dated August 27, 1999

     Securities Purchase Agreement by and between Shoeinvest II, LP and Middle
Bay Oil Company, Inc., dated August 27, 1999

     Securities Purchase Agreement by and between The Prudential Insurance
Company of America and Middle Bay Oil Company, Inc., dated October 19, 1999

                                       4<PAGE>

                                                                   EXHIBIT 10.23

                  AMENDMENT TO SECURITIES PURCHASE AGREEMENT

          This Amendment to Securities Purchase Agreement (the "Amendment")
dated as of November ___, 1999, is entered into by and between MIDDLE BAY OIL
COMPANY, INC., an Alabama corporation ("Corporation") and Shoemaker Family
Partners, LP, a New Jersey limited partnership ("SFP").

                                   RECITALS

     WHEREAS, on August 27, 1999, the Corporation and SFP entered into a certain
Securities Purchase Agreement (the "Agreement"); and

     WHEREAS, the parties hereto wish to amend the Agreement.

     NOW, THEREFORE, in consideration of the mutual promises contained herein
and other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the parties hereto agree as follows:

     1.   All references to "Compass Senior Credit Agreement", "Compass Senior
Debt", and "Compass Senior Debt Documents" in the Agreement and all related
documents (including the Note and Warrants) are hereby replaced with the terms
"Senior Credit Agreement", "Senior Debt", and "Senior Debt Documents"
respectively.

     2.   Section 1.1 is hereby amended to include the following terms:

          "Senior Credit Agreement" means that certain Restated Credit Agreement
dated November ___, 1999, by and among Middle Bay Oil Company, Inc., Enex
Resources Corporation and Middle Bay Production Company, Inc., as borrowers, and
Bank One, Texas, N.A., as agent and a lender, and each other lender or agent now
or hereafter a party thereto and their successors and assigns, and any
replacements, refinancings, amendments, renewals or extensions thereof, whether
with the existing agent and lenders or other agents and lenders."

          "Senior Debt" means all Debt of the Company or any of its Subsidiaries
outstanding under the Senior Debt Documents, including all renewals, extensions,
increases, refinancings, restatements and replacements thereof."

          "Senior Debt Documents" means the Senior Credit Agreement and all
promissory notes, security agreements, mortgages, deeds of trust, assignments,
guaranties and other documents, instruments and agreements executed and
delivered pursuant to the Senior Credit Agreement evidencing, securing,
guaranteeing or otherwise pertaining to the Senior Debt and all other
<PAGE>

obligations arising under the Senior Credit Agreement, as the foregoing may be
amended, renewed, extended, supplemented, increased or otherwise modified from
time to time."

     3.   The following definition in Section 1.1 is hereby deleted in its
entirety and replaced with the following:

          "Senior Lender" means any holder of any Senior Debt."

     4.   Exhibit H.  Exhibit H of the Agreement is hereby deleted in its
          ----------
entirety and replaced with Exhibit H attached hereto.

     5.   Terms Defined in Agreement.  As used herein, each term defined in the
          ---------------------------
Agreement shall have the meaning assigned thereto in the Agreement, unless
expressly provided herein to the contrary.

     6.   Full Force and Effect.  Except with respect to the changes made in
          ----------------------
this Amendment, the terms and provisions of the Agreement are in full force and
effect.

     7.   Notices.  Any notice to be given by any party hereunder to any other
          --------
shall be in writing, mailed by certified or registered mail, return receipt
requested, and shall be addressed to the other parties at the addresses listed
on the signature pages hereof.  All such notices shall be deemed to be given
three (3) days after the date of mailing thereof.

     8.   Binding Effect.  This Amendment shall be binding upon the parties
          ---------------
hereto and their respective successors, personal representatives and permitted
assigns.

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first above written.

"CORPORATION"

MIDDLE BAY OIL COMPANY, INC.

By:___________________________________________
Name: Floyd C. Wilson
Title: President and Chief Executive Officer

Address for Notice:

Middle Bay Oil Company, Inc.
1221 Lamar Street, Suite 1020
Houston, TX 77010
Fax: (713) 650-0352
<PAGE>

"SFP"

SHOEMAKER FAMILY PARTNERS, LP

By:___________________________________________
Name:
Title:

Address for Notice:

Shoemaker Family Partners, LP
60 Brushhill Road
Kinnelon, NJ 07405
Fax: (310) 444-3833
<PAGE>

                                   EXHIBIT H
                     OTHER SECURITIES PURCHASE AGREEMENTS

     Securities Purchase Agreement by and between 3TEC Energy Company L.L.C. and
Middle Bay Oil Company, Inc., dated July 1, 1999

     Securities Purchase Agreement by and between Shoeinvest II, LP and Middle
Bay Oil Company, Inc., dated August 27, 1999

     Securities Purchase Agreement by and between The Prudential Insurance
Company of America and Middle Bay Oil Company, Inc., dated October 19, 1999

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