Document:

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                                                                     EXHIBIT 4.7
                             SUBORDINATION AGREEMENT

         WHEREAS, WEDGE Energy Services, L.L.C., a Delaware limited liability
company ("WEDGE") intends to lend South Texas Drilling & Exploration, Inc.
("SOTX") the sum of $9,000,000.00 evidenced by a Subordinated Note of even date
herewith (the "Subordinated Note"); and

         WHEREAS, the American Bank, N.A. has entered into a Loan Agreement,
(the "Loan Agreement"), with SOTX under which SOTX borrowed $3,000,000.00,
evidenced by one or more notes issued under the Loan Agreement (the "Notes")
which Notes are to be secured by certain real estate and assets of Pioneer
Drilling Co., Ltd. ("Pioneer", which is a partnership comprised of entities
which are wholly owned by SOTX) pursuant to a Deed of Trust and Security
Agreement (the "Security Agreement"). The Loan Agreement, Notes and Security
Agreement and any renewals and extensions thereof, are collectively referred to
herein as the "Superior Indebtedness"); and

         WHEREAS, WEDGE has agreed to subordinate the Subordinated Note and any
renewals and extensions thereof (the "Inferior Indebtedness") to the Superior
Indebtedness:

         NOW, THEREFORE, KNOW ALL MEN BY THESE PRESENTS, that WEDGE, in
consideration of the premises, and in consideration of the sum of TEN AND NO/100
DOLLARS ($10.00) and other good and valuable consideration, the receipt and
sufficiency of which consideration is hereby acknowledged, HAS COVENANTED AND
AGREED, and does hereby COVENANT AND AGREE, that the Inferior Indebtedness shall
be, and the same is hereby made subject and inferior to the Superior
Indebtedness.

         WEDGE further agrees that it will not receive, collect or seek to
collect any amount owing under the Inferior Indebtedness until all of the
Superior Indebtedness is paid in full.

         WEDGE further agrees to take all action necessary to convert the
Inferior Indebtedness into equity in SOTX as soon as shareholder approval has
been obtained.

         IN WITNESS WHEREOF, this instrument has been executed by WEDGE
effective the 30th day of March, 2001.

                                   WEDGE ENERGY SERVICES, L.L.C.

                                   By:  /s/   James M. Tidwell
                                      ------------------------------------------
                                               James M. Tidwell, Vice President

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                                                                     EXHIBIT 4.8

                             SUBORDINATION AGREEMENT

         WHEREAS, WEDGE Energy Services, L.L.C., a Delaware limited liability
company ("WEDGE") intends to lend South Texas Drilling & Exploration, Inc.
("SOTX") the sum of $9,000,000.00 evidenced by a Subordinated Note of even date
herewith (the "Subordinated Note"); and

         WHEREAS, the Frost National Bank ("Bank") has outstanding two loans in
the amounts of $1,000,000 (under a note dated March 20, 2001) and $9,000,000
(under a note dated August 11, 2000) to Pioneer Drilling Co., Ltd. and/or SOTEX
(which loans are collectively referred to herein as the "Frost Superior
Indebtedness"); and

         WHEREAS, WEDGE has agreed to subordinate the Subordinated Note and any
renewals and extensions thereof (the "Inferior Indebtedness") to the Superior
Indebtedness:

         NOW, THEREFORE, KNOW ALL MEN BY THESE PRESENTS, that WEDGE, in
consideration of the premises, and in consideration of the sum of TEN AND NO/100
DOLLARS ($10.00) and other good and valuable consideration, the receipt and
sufficiency of which consideration is hereby acknowledged, HAS COVENANTED AND
AGREED, and does hereby COVENANT AND AGREE, that the Inferior Indebtedness shall
be, and the same is hereby made subject and inferior to the Superior
Indebtedness.

         WEDGE further agrees that it will not receive, collect or seek to
collect any amount owing under the Inferior Indebtedness until all of the
Superior Indebtedness is paid in full. WEDGE further agrees to take all action
necessary to convert the Inferior Indebtedness into equity in SOTX as soon as
shareholder approval has been obtained.

         IN WITNESS WHEREOF, this instrument has been executed by WEDGE
effective the 30th day of March, 2001.

                                     WEDGE ENERGY SERVICES, L.L.C.

                                     By:  /s/   James M. Tidwell
                                        ----------------------------------------
                                                James M. Tidwell, Vice President

                                       -1-<PAGE>   1
                                                                     EXHIBIT 4.9

                            SUBORDINATION AGREEMENT

         WHEREAS, WEDGE Energy Services, L.L.C., a Delaware limited liability
company ("WEDGE") intends to lend South Texas Drilling & Exploration, Inc.
("SOTX") the sum of $9,000,000.00 evidenced by a Subordinated Note of even date
herewith (the "Subordinated Note"); and

         WHEREAS, the Frost National Bank ("Bank") intends to enter into a Loan
Agreement, of even date herewith (the "Loan Agreement"), under which Pioneer
Drilling Co., Ltd. ("Pioneer", which is a partnership comprised of entities
which are wholly owned by SOTX) intends to borrow up to $12,000,000.00,
evidenced by one or more notes issued under the Loan Agreement (the "Notes")
which Notes are to be secured by certain of the assets of Pioneer pursuant to a
Security Agreement of even date herewith (the "Security Agreement"). The Loan
Agreement, Notes and Security Agreement and any renewals and extensions thereof,
are collectively referred to herein as the "Frost Superior Indebtedness"); and

         WHEREAS, WEDGE has agreed to subordinate the Subordinated Note and any
renewals and extensions thereof (the "Inferior Indebtedness") to the Superior
Indebtedness:

         NOW, THEREFORE, KNOW ALL MEN BY THESE PRESENTS, that WEDGE, in
consideration of the premises, and in consideration of the sum of TEN AND NO/100
DOLLARS ($10.00) and other good and valuable consideration, the receipt and
sufficiency of which consideration is hereby acknowledged, HAS COVENANTED AND
AGREED, and does hereby COVENANT AND AGREE, that the Inferior Indebtedness shall
be, and the same is hereby made subject and inferior to the Superior
Indebtedness.

         WEDGE further agrees that it will not receive, collect or seek to
collect any amount owing under the Inferior Indebtedness until all of the
Superior Indebtedness is paid in full. WEDGE further agrees to take all action
necessary to convert the Inferior Indebtedness into equity in SOTX as soon as
shareholder approval has been obtained.

         IN WITNESS WHEREOF, this instrument has been executed by WEDGE
effective the 30th day of March, 2001.

                                    WEDGE ENERGY SERVICES, L.L.C.

                                    By:  /s/   James M. Tidwell
                                       -----------------------------------------
                                               James M. Tidwell, Vice President

                                      -1-<PAGE>   1
                                                                    EXHIBIT 4.10

                                    AGREEMENT

         THIS AGREEMENT ("Agreement") is made and entered into effective as of
the 18th day of May, 2001, by and among South Texas Drilling & Exploration,
Inc., a Texas corporation (the "Company") and WEDGE Energy Services, L.L.C., a
Delaware limited liability company ("WEDGE").

                                   WITNESSETH:

         WHEREAS, on March 30, 2001, WEDGE purchased from the Company a 4.86%
Convertible Subordinated Debenture, Series A (the "Debenture") for a purchase
price of $9,000,000.00 pursuant to that certain Debenture Purchase Agreement and
Debenture Agreement (collectively known as the "Debenture Agreements"); and

         WHEREAS, the Debenture is convertible, upon the Company obtaining
shareholder approval, into 2,400,000 shares of the $0.10 par value Common Stock
of the Company (the "Common Stock"); and

         WHEREAS, the Company desires to cancel the Debenture by paying a sum
equal to $9,000,000.00 plus accrued interest since March 30, 2001.

         NOW THEREFORE, in consideration of the mutual covenants herein
contained, the Company and WEDGE hereby acknowledge and agree as follows:

         1. WEDGE has received from the Company Nine Million Dollars
($9,000,000.00) plus Fifty Nine Thousand Five Hundred Thirty-Five Dollars
($59,535.00), such sum being the amount of accrued interest under the Debenture
since March 30, 2001 to the date hereof, such amounts in the aggregate
constituting full payment of all amounts owing under the Debenture.

         2. The Debenture is hereby cancelled, and all obligations, rights or
duties owed to or held by WEDGE or the Company under the Debenture or Debenture
Agreements are hereby terminated without additional obligation, including,
without limitation, the right of WEDGE to convert the Debenture into 2,400,000
shares of Common Stock.

         3. WEDGE shall have no further recourse against the Company under the
Debenture or Debenture Agreements whatsoever.

                            (SIGNATURE PAGE FOLLOWS)

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         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
become effective the day and date first above written.

                                   SOUTH TEXAS DRILLING & EXPLORATION, INC.

                                   By:  /s/   Wm. Stacy Locke
                                      -----------------------------------------
                                              Wm. Stacy Locke, President

                                   WEDGE ENERGY SERVICES, L.L.C.

                                   By:  /s/   R. E. Blohm, Jr.
                                      -----------------------------------------
                                              R. E. Blohm, Jr., Vice President

                                      -2-

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