English Translation Stock Purchase Agreement

Exhibit 10

STOCK PURCHASE AGREEMENT

This Stock Purchase Agreement (hereinafter " Agreement" ) is made and entered into this 25 th day of January, 2005, in the city of Buenos Aires, by and between:

(I) THE TOWER FUND L.P., a corporation duly organized and existing under the laws of the Cayman Islands, recorded with the Public Registry of Commerce of the city of Buenos Aires, on September 18, 1995, under No. 1137, Book No. 53, Volume B, of Foreign Bylaws Registry, hereby represented by Daniel Enrique Garceda, acting in his capacity as attorney-in-fact, residing at Av. De Mayo 701, piso 8, Ciudad Autf3noma de Buenos Aires; (" Seller" ); party of the first part; and

(II) APCO ARGENTINA INC., a corporation duly organized and existing under the laws of Cayman Island, recorded with the Public Registry of Commerce of the city of Buenos Aires, on May 7, 2001, under No. 1074, Book No. 56, Volume B, of Foreign Bylaws Registry, hereby represented by Thomas Bueno, acting in his capacity as President, residing at Maipfa 1300, piso 8, Ciudad Autf3noma de Buenos Aires (hereinafter " APCO" );

(III) NETHERFIELD CORPORATION, SUCURSAL TIERRA DEL FUEGO, ANTARTIDA E ISLAS DEL ATLANTICO SUR, a branch of Netherfield Corporation, a corporation duly organized and existing under the laws of the British Virgin Islands, recorded with the Controlling Office of Legal Entities [ Inspeccif3n General de Justicia ] in and for the Province of Tierra del Fuego, Ante1rtida e Islas del Atle1ntico Sur , on December 20, 2004, in the Book of Foreign Business Entities No. 1, under No. 012, Page 006, for the year 2004, hereby represented by Verf3nica Beatriz Canalez, acting in her capacity as legal representative, residing at Cervif1o 4449, piso 4, Ciudad Autf3noma de Buenos Aires, (hereinafter " NETHERFIELD" ); and

(IV) ROCH S.A., a corporation duly organized and existing under the laws of the Argentine Republic, recorded with the Public Registry of Commerce of the city of Buenos Aires, on April 26, 1990, under No. 2360, Book No. 107, Volume A on Corporations, hereby represented by Ricardo Omar Chacra, acting in his capacity as President, residing in Av. Eduardo Madero 1020, piso 21, Ciudad Autf3noma de Buenos Aires (hereinafter " ROCH" ); parties of the second part. (APCO, NETHERFIELD and ROCH shall be collectively referred to as " Purchasers" , and Purchasers and Seller together shall be referred to as " Parties" .

WITNESSETH:

(A) WHEREAS, Seller owns ONE HUNDRED, FORTY-THREE THOUSAND, EIGHT HUNDRED, AND FIFTY-THREE (143,853) shares of common stock - with a face value of $1 each, entitling to one vote per share- in Rio Cullen-Las Violetas S.A. (" Rio Cullen-Las Violetas" or " Company" ), a corporation duly organized and existing under the laws of Argentina, such number of shares representing 100% of the issued and outstanding stock of the Company; as described in 2.1 hereof;

(B) WHEREAS, Seller wishes to sell to Purchasers and Purchasers wish to purchase from Seller all of the Shares of Stock, upon the terms and subject to the conditions hereinafter set forth;

NOW THEREFORE, in consideration of the mutual covenants and agreements herein contained, it is hereby agreed as follows:

ARTICLE I
DEFINITIONS

1.1 Definitions

The following terms, when used herein, shall have the following meanings:

" Agreement" shall mean any contract, arrangement, negotiable instrument, undertaking, agreement, obligation or legally binding and enforceable agreement, whether in writing or otherwise, to which the Company is a party, or whereby the Company is subject to obligations or has offered collateral, including any and all amendments thereto;

" Antitrust Authority" shall mean the National Antitrust Commission having authority over antitrust matters or any relevant authority that may thereafter replace it;


" Areas" shall mean the areas under the concession agreement for hydrocarbon production, supplementary exploration and development known as CA-12 " Redo Cullen" , CA-13 " Las Violetas" , and CA-14 " La Angostura" , all of which are located in the Province of Tierra del Fuego, within the scope established by Executive Orders No. 1581/91, 1580/91 and 1579/91, respectively;

" Argentina" shall mean the Argentine Republic;

" Assets" shall mean all types of assets and property (whether real or personal property, assets subject to registration or free from registration, as well as intangible assets), belonging to the Company;

" Authority" shall mean any governmental authority of any state or political subdivision, including the national, provincial or municipal government of Argentina or any of its political subdivisions, as well as any entity within such territory that exercises executive, legislative, judicial, regulatory or administrative powers of government;

" Closing" shall have the meaning ascribed to it in section 2.5 hereof;

" Closing Date" shall mean the date on which Closing shall take place;

" Company" has been defined in the Preambles above;

" Concessions" shall mean the concessions for hydrocarbon production in the AREAS, authorizing the carrying out of activities relating to hydrocarbon exploration, supplementary production and development, pursuant to Argentine Law No. 17.319, as amended and regulated, and Executive Orders No. 1580/91, 1581/91 and 1579/91.

" Dispet" shall mean Dispet S.A.;

" Dollars o US$" shall mean the legal tender in the United States of America;

" Excluded Contingencies" shall mean all the contingencies and/or concepts contemplated in the Agreement for Excluded Contingencies entered into on the date hereof by APCO, NETHERFIELD, ROCH, THE TOWER FUND L.P., RIO CULLEN-LAS VIOLETAS and COMPAd1cdA PAPELERA SARANDcd S.A., (hereinafter, the " Agreement for Excluded Contingencies" ), including, but not limited to, (i) environmental, labor, tax and royalty-related contingencies relating to the UTE, the Concessions and/or the Areas, (ii) the contingencies and/or concepts contemplated in 2.6.B.5(a), (b), (c) and (d); (iii) the contingencies and/or concepts specified in all the Annexes to the Agreement for Excluded Contingencies;

" Financial Statements" shall mean the financial statements of the Company, audited by Alberto G. Maquieira, on June 30, 2004, together with their notes and annexes, prepared in accordance with applicable legal rules and GAAPs;

" GAAPs" shall mean the generally accepted accounting principles pursuant to the professional standards set by the Public Accountants' Professional Association in and for the city of Buenos Aires, applied on a consistent basis throughout the relevant period;

" Law" shall mean any law, executive order, resolution, regulation, code, rule, ordinance, request, or proceeding approved, adopted, enacted or enforced in Argentina or by any Argentine Authority.

" Line of Business" shall mean the business and activities carried on by the Company pursuant to its share in the UTE and/or in the Concessions, on a consistent basis with usual business practices and standards;

" Loss" shall mean any loss, payment (either in cash or in kind), money damages, sanctions, liabilities, obligations, penalties, fines, judgments, arbitration awards, costs, expenses and disbursements (including costs and fees of attorneys, accountants and court experts) resulting from a claim or action brought in relation to the foregoing, provided they cause a Material Adverse Effect to the Company;

" Material Adverse Effect" shall mean any change or effect that is materially adverse to Company' s assets, liabilities or transactions by reason of an event or circumstance originating prior to Closing, to the extent such event or circumstance (i) has not been stated or included in the Financial Statements, (ii) does not result from a discrepancy between the methods used to calculate liabilities and provisions when preparing the Company' s Financial Statements, including, without limitation the method used to calculate applicable taxes, exchange rates, etc., to the extent such methods are consistent with GAAPs in force form time to time, (iii) has not been reported in the Minutes of the Board of Directors' Meeting of the company as of


the date hereof; (iv) does not result from the events or circumstances set forth in the annexes attached hereto; (v) does not result from direct or indirect amendments to the Law;

" Papelera Saranded" shall mean Compaf1eda Papelera Saranded S.A.;

" Party" shall mean Purchasers or Seller severally;

" Parties" shall designate both Purchasers and Seller together;

" Person" shall mean any individual, general partnership, joint stock company, unincorporated association, company, joint venture, Authority or any other entity of any type whatsoever (organized or existing under the laws of Argentina or under the laws of another jurisdiction).

" Pesos or " $"" shall mean the legal tender in Argentina.

" Purchase Price" is defined in 2.2 hereinbelow.

" Purchasers" has been defined in the commencement above;

" Seller" has been defined in the commencement above.

" Shares of Stock" shall mean ONE HUNDRED, FORTY-THREE THOUSAND, EIGHT HUNDRED, AND FIFTY-THREE (143,853) nominative, non-endorsable, shares of common stock of Rio Cullen- Las Violetas owned by Seller and representing 100% of the Company' s capital stock and voting power; as well as all political and economic rights relating to or inherent in such Shares of Stock, including, but not limited to: (a) all rights resulting from any revocable or irrevocable capital contributions on account of future capital increases paid by Seller to the Company on or before the Closing date, not capitalized as of the Closing date, and (b) all rights relating to dividends accrued as of the Closing date, provided such dividends have not been paid out to Seller as of such date.

" Taxes" shall mean all withheld taxes, charges, rates, levies or other contributions, including, without limitation, net income, gross income, sales, use, ad valorem , value added, transfer, franchise, individual income, license, withholding, payroll, employment, excise, succession, recruitment, stamp and other property taxes or any other tax of any kind whatsoever, such as, customs duties, rates, contributions or charges, and/or the obligations to withhold taxes, whether current or future, including any interest, penalty, or addition thereto imposed by an Argentine Tax Authority, including any Tax Authority having local jurisdiction as well as any political subdivision, agency or similar entity of an Argentine Tax Authority having national or local jurisdiction.

' Transaction" is defined in 2.1.

" Undeclared Liabilities" shall mean all those obligations and liabilities of the Company in favor of any Person, originating prior to Closing, provided always that they have been the cause of a Material Adverse Effect and that (i) they have not been accounted for in the Annexes to this Agreement, or (ii) they have originated after the preparation of said Financial Statements and do not relate to the Line of Business. Excluded Contingencies shall not be considered " Undeclared Liabilities" .

" UTE" shall mean the Temporary Business Venture identified as " Rio Cullen-Las Violetas S.A., San Enrique Petrolera S.A., DPG S.A., Compaf1eda Papelera Saranded S.A., Dispet S.A., Roch S.A.-Unif3n Transitoria de Empresas" , organized for the production, supplementary exploration and development of hydrocarbons in Areas CA-12 " Redo Cullen" and CA-13 " Las Violetas" .

1.2 Interpretation

A. Regarding the definitions set forth in 1.1 above, where appropriate, the plural form shall include the singular form and vice versa .

B. The headings of all Articles, Sections and Annexes to this Agreement are inserted for reference purposes only and shall not be considered part of, or affect the meaning or interpretation of any part of this Agreement.

C. All Annexes mentioned herein and attached hereto shall form an integral part hereof.


D. All references in this Agreement to Articles, Clauses or Annexes shall, unless otherwise provided, refer to Articles, Clauses hereof and Annexes attached hereto.

E. The term " or" shall not be deemed to be exclusive.

ARTICLE II
PURCHASE OF SHARES OF STOCK

2.1 Purchase of Shares of Stock

Seller hereby sells, transfers and conveys to Purchasers, and Purchasers purchase and acquire from Seller, the Shares of Stock (hereinafter, the " Transaction" ), subject to the following terms and conditions (including, but not limited to the conditions precedent set out in 2.6 below):

(i) APCO acquires seventy-nine thousand, seven hundred and fifty-two (79,752) nominative, non-endorsable shares of ordinary stock, with a face value of $1 each, entitling to 1 vote per share, which accounts for 55.44% of the Shares of Stock;

(ii) NETHERFIELD acquires thirty-eight thousand, one hundred and fifty (38,150) nominative, non-endorsable shares of ordinary stock, with a face value of $1 each, entitling to 1 vote per share, which accounts for 26.52% of the Shares of Stock;

(iii) ROCH acquires twenty-five thousand, nine hundred and fifty-one (25,951) nominative, non-endorsable shares of ordinary stock, with a face value of $1 each, entitling to 1 vote per share, which accounts for 18.04% of the Shares of Stock.

2.2 Purchase Price

In consideration of the sale, transfer and conveyance of Shares of Stock by Seller to Purchasers, Purchasers shall pay Seller eleven million, two hundred sixty-eight thousand, three hundred and thirty-seven US Dollars (US$ 11,268,337.00) (" Purchase Price" ).

Simultaneously with said transfer of Shares of Stock:

(a) In consideration of all the shares of stock APCO acquires as per provisions of section 2.1.(i) above, APCO shall pay Seller six million, two hundred forty-seven thousand, two hundred and sixty-three US Dollars (US$ 6,247,263.00) through a bank transfer and deposit of readily available funds to the account held in the HSBC Bank U.S.A. No. 605106088, ABA 021001088, Swift Address MRMDUS 33, Account Name: The Tower Fund L.P, free from expenses, charges or taxes assessed on said transfer, which, if any, shall be exclusively borne by APCO;

(b) In consideration of all the shares of stock NETHERFIELD acquires as per provisions of section 2.1.(ii) above, NETHERFIELD shall pay Seller two million, nine hundred eighty-eight thousand, two hundred and sixty-six US Dollars (US$ 2,988,266) through a bank transfer and deposit of readily available funds to the account held in the HSBC Bank U.S.A., No. 605106088, ABA 021001088, Swift Address MRMDUS 33, Account Name: The Tower Fund L.P., free from expenses, charges or taxes assessed on said transfer, which, if any, shall be exclusively borne by NETHERFIELD;

Once all the amounts referred to in (a) and (b) above have been deposited in the account held in the HSBC Bank U.S.A., No. 605106088, ABA 021001088, Swift Address MRMDUS 33, Account Name: The Tower Fund L.P., the Seller shall issue to APCO or NETHERFIELD (as the case may be) a receipt substantially in the form specified in Annex 2.2 .

In consideration of all the shares of stock ROCH acquires as per provisions of section 2.1(iii) above, ROCH shall pay Seller two million, thirty-two thousand, eight hundred and eight US Dollars (US$ 2,032,808.00) (" ROCH Indebtedness" ) on November 15, 2005, through a bank transfer and deposit of freely available funds to the account held in the HSBC Bank U.S.A., No. 605106088, ABA 021001088, Swift Address MRMDUS 33, Account Name: The Tower Fund


L.P., free from expenses, charges or taxes assessed on said transfer, which shall be exclusively borne by ROCH. ROCH shall create a first pledge on all of the Shares of Stock ROCH acquires pursuant to the provisions of 2.1(iii) and other additional amounts relating to the Shares of Stock, as collateral for the payment of ROCH Indebtedness in favor of Seller. The remaining terms and conditions applicable to ROCH Indebtedness and the security interest thereon shall be governed by a Financing Agreement for Purchase Price Balance entered into by ROCH and Seller, simultaneously with this Agreement, in a separate instrument, and a Pledge Agreement to be entered into by ROCH and Seller on the Closing date.

The Purchase Price shall be increased by the amount that Purchases may have to pay Seller pursuant to the provisions of 2.3 and 2.4 below, in the event that the Company collects the referenced Receivables from the Sale of Crude Oil and/or VAT Claim, in whole or in part. The resulting increase in the Purchase Price shall be paid by Purchasers to Seller within the term specified in 2.3 and 2.4, as the case may be, by a bank transfer and deposit of readily available funds to the account held in the HSBC Bank U.S.A. No. 605106088, ABA 021001088, Swift Address MRMDUS 33, Account Name: The Tower Fund L.P., free from any expense, commission, or tax on said transfer payment, which, if any, shall be exclusively borne by Purchasers.

2.3 Receivables from Combustibles Argentinos S.A .

Redo Cullen-Las Violetas, as a member of the UTE, is a creditor of - both directly and indirectly through its share in Dispet S.A., i.e., through its total 50.0769% share in the UTE- Combustibles Argentinos S.A., with a claim amounting to one hundred and seventy-six thousand, two hundred and eighty-six with 90/100 US Dollars (US$ 176,286.90), plus AR$ 64.000 (resulting from bounced checks), plus interest, penalties and other charges thereon, originating in the sale of crude oil to Combustibles Argentinos S.A. (" Receivables from Sales of Crude Oil" ), in the framework of the Producers and Refineries' Agreement on Crude Oil, Petrol and Gasoil Price Stability entered into by Roch S.A., in its capacity as operator and UTE' s representative, and Combustibles Argentinos S.A., on January 2, 2003.

In order for Receivables from the Sale of Crude Oil to be collected it is necessary that the UTE should make further sales of crude oil to Combustibles Argentinos S.A., which is exclusively the UTE' s decision and in connection with which Seller has no right to influence or claim. In the event that the UTE (i) collects Receivables from the Sales of Crude Oil, in whole or in part, or (ii) sells to Combustibles Argentinos S.A. any amount of crude oil, then the Purchase Price shall increase in a dollar-denominated amount equal to all the sums collected by the Company for such sales, the Purchasers having to pay said price to Seller within five (5) days following actual collection. Provisions in (i) or (ii) above shall remain in force and effect for a term of two (2) years next following Closing.

Seller is expressly authorized to assign its rights hereunder upon prior notice to Purchasers.

2.4 Claim for Reimbursement of Value Added Tax

The UTE (a) filed with the Argentine Internal Revenue Office [ Administracif3n Federal de Ingresos Pfablicos ] two claims for the reimbursement of the Value Added Tax concerning tax returns for fiscal periods December 1996; February, April, May, June, July, September, October and November 1997; January, February, April, May, July, August and November 1998; January, April, May and December 1999; January, February, April, June, July, August, October and November 2000; January, February, March, April, June, July and August 2001; and April and May 2002; totalling $624,611.96 (filed on 12/30/2002) plus $4,172,772.01 (filed on 12/23/2003), plus appropriate penalties and interest thereon, and (b) requested from the Argentine Internal Revenue Office the reimbursement to each of the UTE' s members of a withholding amount equat to $760,539.37, for Value Added Tax carried out by Esso to the UTE (the claims referred to in (a) and (b) above shall be collectively referred to as the " VAT Claim" ).

Purchasers agree to instruct the UTE' s operator to seek collection of the VAT Claim, and shall make and instruct the UTE' s operator to make reasonable efforts to that effect. In this regard, Purchasers shall take and instruct the UTE' s operator to take all necessary steps in seeking collection of said VAT Claim, either through administrative and/or out-of-court and/or court proceedings, until effective and full payment thereof.

If said VAT Claim is collected in whole or in part by the UTE or the UTE' s operator, the Purchase Price shall increase in a dollar-denominated amount equal to the aggregate amounts collected by the Company in its capacity as member of the UTE, either directly or indirectly, or through its 50.0769% share, and the Purchasers shall pay said amount within five (5) days next following collection thereof. In the event that payment, in whole or in part, of VAT Claim is made in debt securities, Purchasers shall pay Seller the amount owing hereunder by delivering said debt securities to Seller, unless Seller (i) has notified Purchasers the assignment of its collection rights to a third party, in which case Purchasers shall deliver


said securities to any ...