Document:

<PAGE>

                                                                   EXHIBIT 10.30

                        PRIVATE EQUITY SHELF AGREEMENT

     This Private Equity Shelf Agreement (this "Agreement") is entered into as
of the ___ day of May, 2000, by and among 3TEC Energy Corporation, a Delaware
corporation (the "Company") and EnCap Energy Capital Fund III, L.P., EnCap
Energy Capital Fund III-B, L.P., BOCP Energy Partners, L.P., and Energy Capital
Investment Company PLC (collectively, "Buyer", and each individually a "Buyer
Entity").

                              W I T N E S S E T H:

     WHEREAS, the Company is negotiating the terms of a Second Restated Credit
Agreement to be executed as of the ____ day of May, 2000, by and between the
Company, Enex Resources Corporation, Middle Bay Production Company, Inc., and
Magellan Exploration, LLC, as Borrowers, and Bank One, Texas, N.A., and each of
the financial institutions which is a party thereto (or which may from time to
time become a party thereto), as Lenders, and Bank One, Texas, N.A., as
Administrative Agent (the "Credit Facility"); and

     WHEREAS, the proceeds of the Credit Facility will be used by the Company,
in part, to fund the acquisition of certain properties from C.W. Resources,
Inc., Westerman Royalty, Inc. and Carl A. Westerman (the "CWR Acquisition"); and

     WHEREAS, the Credit Facility requires the Company to make a special
mandatory prepayment of the loan balance no later than December 31, 2000; and

     WHEREAS, if requested by the Company or required under the terms of the
Credit Facility, and subject to the terms and conditions set forth in this
Agreement, the Company desires to issue to Buyer, and Buyer desires to purchase
from the Company, up to 800,000 units (the "Units"), each Unit consisting of (a)
one share of the Company's Series E Preferred Stock, par value $0.02 per share
(the "Preferred Stock") and (b) three warrants, each of which entitles the
holder to purchase one share of the Company's common stock, par value $0.02 per
share ("Common Stock") at an initial exercise price of $0.02 per share (the
"Warrants"); and

     NOW, THEREFORE, in consideration of the premises and the mutual agreements
contained herein, the parties agree as follows:

                                   ARTICLE I

                          AGREEMENT TO PURCHASE UNITS

     Section 1.1.  Agreement to Purchase Units.  Subject to the terms and
                   ---------------------------
conditions contained in this Agreement, Buyer agrees to purchase from the
Company up to 800,000 Units at a purchase price of $25.00 per Unit. The number
of Units to be purchased by Buyer shall be determined by the Company and stated
in the Takedown Notice given pursuant to Section 1.2. Subject to the
satisfaction of the conditions set forth in this Agreement, on the Closing Date
established in accordance with Section 1.2, Buyer shall pay the aggregate
purchase price for the
<PAGE>

Units to the Company and the Company shall issue the Preferred Stock and the
Warrants comprising the Units to Buyer. The aggregate purchase price for the
Units (the "Takedown Amount") shall be paid by wire transfer of immediately
available funds to the account designated by the Company. Each Buyer Entity will
fund the portion of the Takedown Amount, and purchase the portion of the Units,
shown below:

     EnCap Energy Capital Fund III, L.P.       42.4790%
     EnCap Energy Capital Fund III-B, L.P.     32.1269%
     BOCP Energy Partners, L.P.                10.3941%
     Energy Capital Investment Company PLC     15.0000%

     Section 1.2.  Takedown. Under this Agreement, the Company may effect one
                   --------
"Takedown" by giving written notice to Buyer (the "Takedown Notice") stating the
Takedown Amount and the proposed "Closing Date" (which date must be at least 10
business days after the date the Takedown Notice is given and also must be prior
to the Takedown Expiration Date). The "Takedown Expiration Date" shall mean the
earlier of (a) December 31, 2000, (b) the date that the Company consummates a
private or public equity offering (other than an offering of shares in
connection with a merger or acquisition, or an offering to employees under a
stock option or other employee benefit plan), or (c) the date the Company makes
the Special Mandatory Prepayment (as defined in the Credit Facility).

     Section 1.3.  Preferred Stock.  To authorize the Preferred Stock, the
                   ---------------
Company shall adopt and file as necessary with the Secretary of State of
Delaware a Certificate of Designations in the form attached hereto as Exhibit A.
                                                                      ---------
The Company shall not amend the Certificate of Designations without the prior
written consent of Buyer. The Company shall not issue any Preferred Stock except
(a) to Buyer on the Closing Date and (b) after the Closing Date in respect of
dividends on outstanding shares of Preferred Stock.

     Section 1.4.  Warrants.  Each Warrant shall entitle the holder thereof to
                   --------
purchase one share of Common Stock at an initial exercise price of $0.02 per
share. The Warrants will be governed by the terms, and evidenced by certificates
in the form, attached hereto as Exhibit B.
                                ---------

     Section 1.5.  Reservation of Shares.
                   ---------------------

     (a)  From and after the Closing Date, the Company will at all times have
authorized, and reserve and keep available, free from preemptive rights, for the
purpose of enabling it to satisfy any obligation to issue Common Stock upon the
exercise by the holders of the Preferred Stock of their conversion rights, the
number of shares of Common Stock deliverable upon such conversion rights. The
Company covenants that all Common Stock issued by it upon conversion of the
Preferred Stock will, upon issuance in accordance with the terms of this
Agreement and the Certificate of Designations, be fully paid and nonassessable.

     (b)  From and after the Closing Date, the Company will at all times have
authorized, and reserve and keep available, free from preemptive rights, for the
purpose of enabling it to satisfy any obligation to issue Common Stock upon the
exercise of the Warrants, the number of

                                      -2-
<PAGE>

shares of Common Stock deliverable upon exercise of all outstanding Warrants
(whether or not exercisable). The Company covenants that all Common Stock issued
by it upon exercise of Warrants will, upon issuance in accordance with the terms
of this Agreement and the Warrant certificates, be fully paid and nonassessable.

     Section 1.6.  Restriction on Transfer.  Buyer understands and agrees that
                   -----------------------
the Units consisting of Preferred Stock and Warrants to be issued by the Company
to Buyer on the Closing Date, and the Common Stock issuable upon conversion of
the Preferred Stock and exercise of the Warrants (collectively, the
"Securities"), have not been registered under the Securities Act of 1933, as
amended (the "Securities Act") or any state securities laws, and that
accordingly, they will not be fully transferable except as permitted under
various exemptions contained in the Securities Act and applicable state
securities laws, or upon satisfaction of the registration and prospectus
delivery requirements of the Securities Act and applicable state securities
laws. Buyer acknowledges that it must bear the economic risk of its investment
in the Securities for an indefinite period of time since they have not been
registered under the Securities Act and applicable state securities laws and
therefore cannot be sold unless they are subsequently registered or an exemption
from registration is available. Absent an effective registration statement under
the Securities Act and applicable state securities laws covering the disposition
of the Securities, Buyer will not sell, transfer, assign, pledge, hypothecate or
otherwise dispose of any or all of the Securities absent a valid exemption from
the registration and prospectus delivery requirements of the Securities Act and
the registration or qualification requirements of any applicable state
securities laws.

     Section 1.7.   Fees and Expenses.
                    -----------------

     (a)  Upon the execution and delivery of this Agreement by the parties
hereto, the Company shall pay Buyer a standby facility fee equal to $500,000.
The standby facility fee shall be paid by wire transfer of immediately available
funds to an account or accounts designated by Buyer.

     (b)  On the Closing Date, the Company shall pay Buyer a takedown fee equal
to 1 1/2% of the Takedown Amount. This fee, at the Company's option, shall be
paid either (i) by wire transfer of immediately available funds to an account or
accounts designated by Buyer or (ii) by an offset against the purchase price to
be delivered by Buyer to the Company on the Closing Date.

     (c)  The Company shall pay directly or reimburse Buyer for payment of the
reasonable attorneys' fees and expenses of its counsel in connection with the
negotiation, preparation and implementation of this Agreement. The Company shall
pay such reimbursement to Buyer in cash no later than 15 days after Buyer
presents a reasonably detailed written summary of such fees and expenses to the
Company.

     Section 1.8  Credit Facility.  The Company shall require that the Credit
                  ---------------
Facility permit the Company to fulfill its obligations under this Agreement and
the Preferred Stock and the Warrants, including without limitation the
obligations relating to dividends, conversion,

                                      -3-
<PAGE>

redemption and repurchase. The Company shall not permit any amendment or
modification to the Credit Facility that would not permit the Company to fulfill
such obligations. The Company shall use the proceeds from the Takedown to make
the Special Mandatory Prepayment (as defined in the Credit Facility).

                                  ARTICLE II

                        REPRESENTATIONS OF THE COMPANY

     The Company hereby represents and warrants to Buyer as follows:

     Section 2.1  Corporate Existence and Power. The Company (a) is a
                  -----------------------------
corporation, duly organized, validly existing and in good standing under the
laws of the State of Delaware, (b) has all corporate power and authority
necessary to carry on its business as now conducted and as proposed to be
conducted, and (c) is duly qualified as a foreign corporation in all
jurisdictions where such qualification is necessary to conduct its business.

     Section 2.2.  Corporate and Governmental Authorization; Contravention.  The
                   -------------------------------------------------------
execution, delivery and performance of this Agreement by the Company are within
its corporate powers, have been duly authorized by all necessary corporate
action, require no action by or in respect of, or filing with, any governmental
authority (other than the filing of the Certificate of Designations with the
Secretary of State of Delaware), and, except for matters which have been waived
in writing by the appropriate person, do not contravene, or constitute a default
under, any provision of applicable law or of the Company's Certificate of
Incorporation or Bylaws or of any material judgment, injunction, order, decree
or material agreement binding upon the Company or its assets.

     Section 2.3.  Binding Effect. This Agreement constitutes the valid and
                   --------------
binding agreement of the Company, enforceable in accordance with its terms
except as (a) the enforceability hereof may be limited by bankruptcy, insolvency
or similar laws affecting creditors rights generally, and (b) the availability
of equitable remedies may be limited by equitable principles of general
applicability.

     Section 2.4.  SEC Documents. The Company is current in its obligations to
                   --------------
file all periodic reports and proxy statements with the Securities and Exchange
Commission (the "SEC") required to be filed under the Securities Exchange Act of
1934, as amended (the "Exchange Act"). Buyer has had available to it true and
correct complete copies of each report, schedule, registration statement and
definitive proxy statement filed by the Company with the SEC since January 1,
1999, and prior to the date of this Agreement (the "SEC Documents"), which are
all the documents (other than preliminary material) that the Company was
required to file with the SEC since such date. As of their respective dates, the
SEC Documents complied in all material respects with the requirements of the
Securities Act or the Exchange Act as the case may be, and the rules and
regulations of the SEC thereunder applicable to such SEC Documents, and none of
the SEC Documents contained any untrue statement of a material fact or omitted
to state a material fact required to be stated therein or necessary to make the
statements therein, in

                                      -4-
<PAGE>

light of the circumstances under which they were made, not misleading. The
financial statements of the Company included in the SEC Documents comply in all
material respects with the published rules and regulations of the SEC with
respect thereto, and such financial statements (i) were prepared from the books
and records of the Company and its consolidated subsidiaries, (ii) were prepared
in accordance with generally accepted accounting principles applied on a
consistent basis (except as may be indicated therein or in the notes or
schedules thereto) and (iii) present fairly the financial position of the
Company as at the dates thereof.

     Section 2.5. Absence of Undisclosed Liabilities. Except as and to the
                  ----------------------------------
extent disclosed in the SEC Documents filed prior to the date hereof, as of
March 31, 2000, the Company has no material liabilities or obligations (whether
accrued, absolute, contingent, unliquidated, or otherwise, whether or not known
to the Company, and whether due or to become due) of a nature required by
generally accepted accounting principles to be recognized or disclosed in
consolidated financial statements of the Company. Since March 31, 2000, the
Company has not incurred any such liabilities or obligations, other than those
incurred in the ordinary course of business consistent with past practice or
pursuant to or as contemplated by this Agreement.

     Section 2.6.  Absence of Certain Changes.  Except as disclosed in the SEC
                   --------------------------
Documents filed prior to the date hereof, since March 31, 2000, (ai) there has
not been any material adverse change in, or any event or condition that might
reasonably be expected to result in any material adverse change in, the
business, assets, results of operations, condition (financial or otherwise), or
prospects of the Company; (b) the business of the Company has been conducted
only in the ordinary course consistent with past practice; (c) the Company has
not incurred any material liability, engaged in any material transaction, or
entered into any material agreement outside the ordinary course of business
consistent with past practice; and (d) the Company has not suffered any material
loss, damage, destruction, or other casualty to any of its assets (whether or
not covered by insurance).

     Section 2.7. Securities. The Securities will have been duly authorized for
                  ----------
issuance and, when issued and delivered by the Company in accordance with the
provisions of this Agreement, will be validly issued, fully paid, and
nonassessable. The issuance of the Securities under this Agreement is not
subject to any preemptive or similar rights.

                                  ARTICLE III

                           REPRESENTATIONS OF BUYER

     Each Buyer Entity hereby represents and warrants to the Company, but only
as to itself and not as to any other Buyer Entity, and not jointly or severally,
as follows:

     Section 3.1. Existence and Power. Each Buyer Entity (a) is a corporation or
                  -------------------
limited partnership, duly organized, validly existing and in good standing under
the laws of its jurisdiction of formation, (b) has all requisite corporate or
partnership power and authority necessary to carry on its business as it is now
conducted, and (c) is duly qualified as a foreign

                                      -5-
<PAGE>

corporation or partnership in all jurisdictions where such qualification is
necessary to conduct its business.

     Section 3.2. Authorization; Contravention.  The execution, delivery and
                  ----------------------------
performance of this Agreement by each Buyer Entity are within such Buyer
Entity's powers, have been duly authorized by all necessary action, require no
action by or in respect of, or filing with, any governmental authority, and,
except for matters which have been waived in writing by the appropriate person,
do not contravene, or constitute a default under, any provision of applicable
law or of the organizational documents of such entity or of any material
judgment, injunction, order, decree or material agreement binding upon such
Buyer Entity or its assets.

     Section 3.3. Binding Effect. This Agreement constitutes the valid and
                  --------------
binding agreement of each Buyer Entity, enforceable against it in accordance
with its terms except as (a) the enforceability hereof may be limited by
bankruptcy, insolvency or similar laws affecting creditors rights generally, and
(b) the availability of equitable remedies may be limited by equitable
principles of general applicability.

     Section 3.4. Investment Representation. Each Buyer Entity understands that
                  -------------------------
the Securities have not been registered under the Securities Act and that the
Securities are being offered and sold pursuant to an exemption from registration
contained in the Securities Act based in part upon such Buyer Entity's
representations contained in this Agreement. Taking into account its respective
personnel and resources, each Buyer Entity is knowledgeable, sophisticated and
experienced in making, and is qualified to make, decisions with respect to
investments in securities presenting an investment decision like that involved
in the purchase of the Securities, and has requested, received, reviewed and
considered all information such Buyer Entity deems relevant in making an
informed decision to purchase the Securities. Each Buyer Entity is acquiring the
Securities for its own account for investment only and with no present intention
of distributing any of the Securities and has no arrangement or understanding
with any other persons regarding the distribution of the Securities. No Buyer
Entity will, directly or indirectly, offer, sell, pledge, transfer or otherwise
dispose of (or solicit any offers to buy, purchase or otherwise acquire or take
a pledge of) any of the Securities except in compliance with the Securities Act
and applicable state securities laws, the rules and regulations promulgated
thereunder and the terms and conditions hereof. Each Buyer Entity is an
"accredited investor" within the meaning of Rule 501 of Regulation D promulgated
under the Securities Act.

                                   ARTICLE IV

                             CONDITIONS TO CLOSING

     Section 4.1. Conditions Precedent to Obligations of Buyer. The obligations
                  --------------------------------------------
of Buyer to purchase the Units on the Closing Date shall be subject to the
fulfillment on or prior to the Closing Date of each of the following conditions:

                                      -6-
<PAGE>

     (a)  Representations and Warranties. The representations and warranties of
          ------------------------------
the Company contained in Sections 2.1, 2.2, 2.3 and 2.7 of this Agreement shall
be true and correct in all material respects on the Closing Date as if they were
made on such date.

     (b)  Covenants and Agreements Performed. The Company shall have performed
          ----------------------------------
and complied with all covenants and agreements required by this Agreement to be
performed or complied with by it on or prior to the Closing Date, including
without limitation the obligation of the Company to reserve shares of Common
Stock under Section 1.5 of this Agreement.

     (c)  Officer's Certificate. Buyer shall have received a certificate from an
          ---------------------
authorized officer of the Company certifying in such detail as Buyer shall
reasonably request that the conditions set forth in this Section 4.1 have been
fulfilled.

     (d)  Preferred Stock.  The Certificate of Designations in the form set
          ---------------
forth as Exhibit A hereto shall have been filed with the Secretary of State of
         ---------
Delaware and shall not have been amended, modified or repealed in any way.

     (e)  Credit Facility; CWR Acquisition. The Company shall have entered into
          ---------------
the Credit Facility and consummated the CWR Acquisition. The Credit Facility
shall not have been amended or modified in any way that would restrict the
ability of the Company to carry out its obligations under this Agreement or the
terms of the Preferred Stock and the Warrants, including without limitation the
obligations relating to dividends, conversion, redemption and repurchase.

     (f)  Legal Opinion. Buyer shall have received the favorable opinion of
          -------------
counsel for the Company, which counsel shall be reasonably acceptable to Buyer,
and which opinion shall be in form and substance reasonably satisfactory to
Buyer and its counsel.

     (g)  Actions or Proceedings. No action or proceeding shall, on the Closing
          ----------------------
Date, be pending or threatened to restrain, prohibit or obtain damages or other
relief in connection with this Agreement or the consummation of the transactions
contemplated hereby.

     (h)  Legal Prohibition. No statute, rule or regulation shall make
          -----------------
consummation of the transactions contemplated hereby illegal or otherwise
prohibited.

     (i)  Other Matters. Buyer shall have received such other documents,
          -------------
instruments and agreements as it shall reasonably request.

     Section 4.2.  Conditions Precedent to Obligations of the Company.  The
                   --------------------------------------------------
obligations of the Company to issue the Units to Buyer on the Closing Date shall
be subject to the fulfillment on or prior to the Closing Date of each of the
following conditions:

     (a)  Representations and Warranties.  The representations and warranties of
          ------------------------------
Buyer contained in this Agreement shall be true and correct in all material
respects on the Closing Date as if they were made on such date.

                                      -7-
<PAGE>

     (b)  Covenants and Agreements Performed.  Buyer shall have performed and
          ----------------------------------
complied with all covenants and agreements required by this Agreement to be
performed or complied with by it on or prior to the Closing Date.

     (c)  Officer's Certificate.  The Company shall have received a certificate
          ---------------------
executed on behalf of all of the Buyer Entities certifying in such detail as the
Company shall reasonably request that the conditions set forth in this Section
4.2 have been fulfilled.

     (d)  Actions or Proceedings.  No action or proceeding shall, on the Closing
          ----------------------
Date, be pending or threatened to restrain, prohibit or obtain damages or other
relief in connection with this Agreement or the consummation of the transactions
contemplated hereby.

     (e)  Legal Prohibition. No statute, rule or regulation shall make
          -----------------
consummation of the transactions contemplated hereby illegal or otherwise
prohibited.

     (f)  Other Matters.  The Company shall have received such other documents,
          -------------
instruments and agreements as it shall reasonably request.

                                   ARTICLE V

                    EXCHANGE OF PREFERRED STOCK AND WARRANTS

     Section 5.1. Exchange Option.  Subject to the terms and conditions of this
                  ---------------
Article V, if the Company makes a Private Equity Issuance (as defined below)
while Buyer owns shares of Preferred Stock, Buyer shall have the option to
exchange some or all of its Preferred Stock and Warrants for the equity security
being issued by the Company. A "Private Equity Issuance" shall mean the issuance
by the Company of equity securities (the "New Securities") other than (i) in
connection with a merger or acquisition, (ii) to employees under a stock option
or other employee benefit plan, or (iii) pursuant to a registration statement
that has been declared effective by the SEC under the Exchange Act.

     Section 5.2. Exchange Procedure. No less than 15 days prior to the closing
                  ------------------

of a Private Equity Issuance, the Company shall provide Buyer with (i) written
notice describing the New Securities, the price of the New Securities, the terms
of the offering, and the scheduled closing date, and (ii) all other written or
electronic materials that have been provided to prospective purchasers of the
New Securities. Buyer shall notify the Company within ten days of its receipt of
these materials whether Buyer desires to exchange all or a portion of its
Preferred Stock and Warrants for New Securities. If Buyer desires to exchange
less than all of its Preferred Stock, Buyer's notice shall set forth the amount
to be exchanged. If Buyer fails to deliver a notice within the time period
specified above, Buyer will be deemed to have elected not to exchange its
Preferred Stock and Warrants for New Securities. However, if the terms of the
equity offering are materially changed from the terms described in the Company's
original notice, the Company shall not issue the New Securities without first
delivering a new notice to Buyer, to which Buyer may respond, all as provided in
the first four sentences of this Section 5.2. If Buyer elects to exchange its
Preferred Stock and Warrants, then at the closing of the Company's equity
offering

                                      -8-
<PAGE>

Buyer shall surrender to the Company the certificates representing the Preferred
Stock and Warrants to be exchanged and the Company shall issue to Buyer
certificates representing the number of New Securities determined in accordance
with Section 5.3.

     Section 5.3. Exchange Ratio. At the closing of the Private Equity Issuance,
                  --------------
the Company shall issue to Buyer the amount of New Securities that Buyer would
be receiving if Buyer were investing an amount in cash equal to the liquidation
value of the Preferred Stock being exchanged (including the amount of all
accumulated or accrued dividends that have not been paid). To the extent Buyer
owns any Warrants at the time of such exchange, then Buyer shall also surrender
to the Company, in consideration for such New Securities, three Warrants per
share of Preferred Stock being surrendered, counting only shares of Preferred
Stock issued on the Closing Date and not counting shares of Preferred Stock
issued subsequently in payment of dividends or otherwise.

                                   ARTICLE VI

                                 MISCELLANEOUS

     Section 6.1. Notices. All notices, requests and other communications to any
                  -------
party hereunder shall be in writing and shall be given to such party at its
address or telecopy number set forth on the signature pages hereof or such other
address or telecopy number as such party may hereafter specify for the purpose
by notice to the other party. Each such notice, request or other communication
shall be effective (a) if given by telecopy, when such telecopy is transmitted
to the telecopy number specified in this Section 6.1 and the appropriate answer
                                         -----------
back is received or receipt is otherwise confirmed, (b) if given by mail, three
(3) business days after deposit in the US mail with first class postage prepaid,
addressed as aforesaid, or (c) if given by any other means, when delivered at
the address specified in this Section 6.1.
                              -----------

     Section 6.2.  Indemnification.  The Company  agrees to indemnify and hold
                   ---------------
harmless each Buyer Entity and its shareholders, and their respective directors,
officers, employees, agents, successors and assigns (collectively, the
"Indemnified Parties") from and against (and will reimburse each Indemnified
Party as the same are incurred) any and all liabilities, losses, damages, costs
and expenses of any kind (including, without limitation, reasonable attorneys'
fees and disbursements that may be incurred by or asserted or awarded against
any Indemnified Party, in each case arising out of or in connection with or by
reason of (including, without limitation, in connection with any investigation,
litigation or proceeding or preparation of a defense in connection therewith)
(a) any breach by the Company of any of its representations, warranties,
covenants or agreements contained in this Agreement or (b) any matters
contemplated by this Agreement.

     Section 6.3.  Amendment and Waiver.  This Agreement may not be modified or
                   --------------------
amended except by an instrument or instruments in writing signed by the party
against whom enforcement of any such modification or amendment is sought. No
failure or delay by any holder of Securities in exercising any right, power or
privilege hereunder shall operate as a waiver thereof nor shall any single or
partial exercise thereof preclude any other or further

                                      -9-
<PAGE>

exercise thereof or the exercise of any other right, power or privilege. The
rights and remedies herein provided shall be cumulative and not exclusive of any
rights or remedies provided by law.

     Section 6.4.  Entire Agreement.  This agreement and the exhibits hereto
                   ----------------
collectively represent the final agreement between the parties and may not be
contradicted by evidence of prior, contemporaneous or subsequent oral agreements
between the parties. There are no unwritten oral agreements between the parties
with respect to the subject matter hereof.

     Section 6.5.  Binding Effect; Assignment; No Third Party Benefit.  This
                   --------------------------------------------------
Agreement shall be binding upon and inure to the benefit of the parties hereto
and their respective successors and permitted assigns.  Except as otherwise
expressly provided in this Agreement, neither this Agreement nor any of the
rights, interests, or obligations hereunder shall be assigned by any of the
parties hereto without the prior written consent of the other parties.  Nothing
in this Agreement, express or implied, is intended to or shall confer upon any
person other than the parties hereto, and their respective successors and
permitted assigns, any rights, benefits, or remedies of any nature whatsoever
under or by reason of this Agreement.

     Section 6.6. Severability. If any provision of this Agreement is held to be
                  ------------
unenforceable, this Agreement shall be considered divisible and such provision
shall be deemed inoperative to the extent it is deemed unenforceable, and in all
other respects this Agreement shall remain in full force and effect; provided,
however, that if any such provision may be made enforceable by limitation
thereof, then such provision shall be deemed to be so limited and shall be
enforceable to the maximum extent permitted by applicable law.

     Section 6.7. GOVERNING LAW. THIS AGREEMENT AND THE TRANSACTION DOCUMENTS
                  -------------
SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS OF THE STATE OF
TEXAS.

     Section 6.8.  Counterparts.  This Agreement may be signed in any number of
                   ------------
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

                                      -10-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed by their respective duly authorized officers on the day and year
first above written.

                                    3TEC ENERGY CORPORATION

                                    By:   ______________________________
                                    Name: R. A. Walker
                                    Title: President

                                    Address for Notice:

                                    3TEC Energy Corporation
                                    Two Shell Plaza
                                    777 Walker, Suite 2400
                                    Houston, TX 77002
                                    Fax: (713) 222-6418

                                    ENERGY CAPITAL INVESTMENT COMPANY
                                    PLC

                                    By: _________________________________
                                        Name: David B. Miller
                                        Title: Authorized Representative

                                    Address for Notice:

                                    c/o EnCap Investments L.L.C.
                                    3811 Turtle Creek Blvd., Suite 1080
                                    Dallas, Texas 75219
                                    Attention: David B. Dunton
                                    Fax:  (214) 599-0200

                                      -11-
<PAGE>

                         ENCAP ENERGY CAPITAL FUND III, L.P.

                         By:  ENCAP INVESTMENTS L.L.C., General Partner

                              By:  _____________________________________
                                   Name:  David B. Miller
                                   Title: Managing Director

                         Address For Notice:

                         c/o EnCap Investments L.L.C.
                         3811 Turtle Creek Blvd., Suite 1080
                         Dallas, Texas 75219
                         Attention:  David B. Dunton
                         Fax:  (214) 599-0200

                         ENCAP ENERGY CAPITAL FUND III-B, L.P.

                         By:  ENCAP INVESTMENTS L.L.C., General Partner

                              By:  _____________________________________
                                   Name:  David B. Miller
                                   Title: Managing Director

                         Address For Notice:

                         c/o EnCap Investments L.L.C.
                         3811 Turtle Creek Blvd., Suite 1080
                         Dallas, Texas 75219
                         Attention:  David B. Dunton
                         Fax:  (214) 599-0200

                                      -12-
<PAGE>

                         BOCP ENERGY PARTNERS, L.P.

                         By:  ENCAP INVESTMENTS L.L.C., Manager

                              By:  ____________________________
                                   Name:  David B. Miller
                                   Title: Managing Director

                         Address For Notice:

                         c/o EnCap Investments L.L.C.
                         3811 Turtle Creek Blvd., Suite 1080
                         Dallas, Texas 75219
                         Fax:  (214) 599-0200

                                      -13-<PAGE>

                                                                   Exhibit 10.19

                           Cummings Properties, LLC
                                 Standard Form
                             Amendment to Lease #2

In connection with a lease currently in effect between the parties at 157H
Cummings Center, Beverly, Massachusetts, executed on April 30, 1998 and
terminating December 31, 2006, and in consideration of the mutual benefits to be
herefrom, Cummings Properties, LLC, LESSOR, and Wakefield Engineering, Inc.,
LESSEE, hereby agree to amend said lease as follows:

1.   The size of the leased premised is hereby decreased by approximately 3,917
square feet (including 15.4% common area), from approximately 19,798 square feet
(including 15.4% common area) to a new total of approximately 15,881 square feet
(including 15.4% common area), with the relinquishment of the cross-hatched area
shown on the mutually agreed upon plan attached hereto (the "relinquished
area").

2    LESSOR, at LESSOR's cost, shall modify 157H Cummings Center according to
the attached plan.

3.   LESSOR or LESSOR's designated moving company shall, at LESSOR's expense,
move LESSEE's furniture, furnishings and equipment from the relinquished area to
other areas designated by LESSEE within 157H Cummings Center.

4.   LESSEE shall continue to have shared access to the loading dock at 159K
Cummings Center.

5.   Notwithstanding Section 22 of the lease and Paragraph P of the Rider to
Lease, LESSOR waives its right to relocate LESSEE to another facility.

6.   LESSEE's quarterly cost for its proportionate share of the trash billing
shall remain at $320.00 for the remainder of the initial lease term.

7.   At any one time during the initial term of this lease, LESSEE has the
option to lease additional space of approximately 3,917 square feet (including
15.4% common area.)  LESSEE shall give LESSOR written notice of such
requirement, and shall then execute LESSOR's standard form amendment to lease
adding such additional space at LESSEE's then current rental rate within three
business days of LESSOR's written notice to LESSEE that said space will be
available. LESSOR shall offer such space within six months after receipt of
written notice from Lessee.

8.   Notwithstanding monthly rent as provided below, LESSEE may deduct $1,375.00
per month from each monthly rental payment due from April 1, 2000 through March
30, 2001 (only), provided LESSOR receives each such monthly payment on or before
the first day of the month for which that rent is due and LESSEE is not
otherwise in default of the lease or in arrears of any rent or invoice payments.
Time is of the essence.

This amendment shall not bind either party in any manner until it has been
executed by both parties. All other terms, conditions and covenants of the
present lease shall continue to apply except that adjusted base rent shall be
increased* by $48,545.55 annually, from a total of $245,367.59 to a new annual
total of $196,822.04 or $16,401.83 per month. Annual base rent for purposes of
computing any future escalations thereon be $187,986.66. This amendment shall be
effective April 1, 2000 and shall continue through the balance of the lease and
any extensions thereof unless further modified by written amendment(s).
In Witness Whereof, LESSOR and LESSEE have hereunto set their hands and common
seals this- 29th day of March, 2000.

LESSOR:  CUMMINGS PROPERTIES, LLC            LESSEE: WAKEFIELD ENGINEERING INC.

By: /s/ Douglas Stephens                     By: /s/ James Poliekiez
    -----------------------                      ------------------------
    Executive Vice President                 James Polakiewicz

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