FIRST AMENDMENT Dated as of March 3, 2005 to NOTE PURCHASE AGREEMENT

Exhibit 10.1

E XECUTION C OPY

P ENN V IRGINIA O PERATING C O ., LLC

AND

P ENN V IRGINIA R ESOURCE P ARTNERS , L.P.

F IRST A MENDMENT

Dated as of March 3, 2005

to

N OTE P URCHASE A GREEMENT

Dated as of March 27, 2003

and

P ARENT G UARANTY

Dated as of March 27, 2003

F IRST A MENDMENT TO N OTE P URCHASE A GREEMENTS AND P ARENT G UARANTY

T HIS F IRST A MENDMENT dated as of March 3, 2005 (the or this “First Amendment” ) to (i) the Note Purchase Agreements (as hereinafter defined) and (ii) the Parent Guaranty (as hereinafter defined) is among P ENN V IRGINIA O PERATING C O ., LLC, a Delaware limited liability company (the “Company” ), P ENN V IRGINIA R ESOURCE P ARTNERS , L.P., a Delaware limited partnership (the “Parent Company” ), and each of the institutions which is a signatory to this First Amendment (collectively, the “Noteholders” ).

R E C I T A L S :

A. The Company, the Parent Company and each of the Noteholders have heretofore entered into separate and several Note Purchase Agreements, each dated as of March 27, 2003 (collectively, the “Note Purchase Agreements” ). The Company has heretofore issued $90,000,000 aggregate principal amount of its 5.77% Senior Notes due March 27, 2013 (the “Notes” ) pursuant to the Note Purchase Agreements. The Noteholders are the holders of      % of the outstanding principal amount of the Notes.

B. The Parent Company guaranteed for the benefit of the Noteholders the payment and performance of the Notes by the Company pursuant to that certain Parent Guaranty dated as of March 27, 2003 (the “Parent Guaranty” ).

C. The Company and the Parent Company desire to acquire the equity interests in Cantera Gas Resource, LLC and to engage in the oil and gas midstream business and in connection therewith would require certain amendments to the Note Purchase Agreements and Parent Guaranty.

D. The Company, the Parent Company and the Noteholders now desire to amend the Note Purchase Agreements and the Parent Guaranty in the respects, but only in the respects, hereinafter set forth.

E. Capitalized terms used herein shall have the respective meanings ascribed thereto in the Note Purchase Agreements unless herein defined or the context shall otherwise require.

F. All requirements of law have been fully complied with and all other acts and things necessary to make this First Amendment a valid, legal and binding instrument according to its terms for the purposes herein expressed have been done or performed.

N OW , T HEREFORE , upon the full and complete satisfaction of the conditions precedent to the effectiveness of this First Amendment set forth in Section 3.1 hereof, and in consideration of good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the Company, the Parent Company and the Noteholders do hereby agree as follows:

S ECTION 1. A MENDMENTS .

Section 1.1. The following shall be added as a new Section 1.4 of the Note Purchase Agreements:

Section 1.4. Changes in Interest Rate. (a) From and including the First Amendment Effective Date to and until the date on which the outstanding principal amount of the Notes has been paid in full, the interest rate on the Notes shall be increased by 25 basis points (0.25%) to 6.02% per annum.

(b) (1) In addition to the adjustment in the foregoing paragraph (a), if as of March 15 or September 15 of any year the then most recent credit rating of the Notes that is in full force and effect (not having been withdrawn) is not equal to or better than a Note Investment Grade Rating, then as of the immediately following Interest Rate Adjustment Date, to and until the Interest Rate Adjustment Date immediately following the date on which the Company obtains from at least one Rating Agency a Note Investment Grade Rating, the Notes shall bear interest at the Adjusted Interest Rate; provided that, the failure of the Company to receive and deliver to the holders of the Notes a rating pursuant to Section 9.9 shall be deemed a rating less than the Note Investment Grade Rating. If after such date the Company fails to maintain from such Rating Agency such Note Investment Grade Rating in respect of the Notes the adjustments set forth in this Section 1.4(b) shall again apply.

(2) The Company shall during the period from and including March 15 to and including March 20 and during the period from and including September 15 to and including September 20 of each year notify the holders of the Notes in writing, sent in the manner provided in Section 18 , that either it has obtained a Note Investment Grade Rating which is in full force and effect or that it does not have a Note Investment Grade Rating, which written notice shall be accompanied by evidence satisfactory to the Required Holders to such effect and certifying the interest rate to be payable in respect of the Notes in consequence thereof.

(c) Each holder of a Note shall, at the Company’s expense, use reasonable efforts to cooperate with any reasonable request made by the Company in connection with any rating appeal or application.

(d) The fees and expenses of the Rating Agency and all other costs incurred in connection with obtaining or appealing a rating of the Notes pursuant to this Section 1.4 shall be borne by the Company.

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Section 1.2. Section 7.1 of the Note Purchase Agreements shall be and is hereby amended by deleting the “.” in paragraph (i) thereof and replacing the same with “; and” and by adding to the end thereof a new paragraph (j) to read as follows:

(i) Permitted Acquisition— promptly, and in any event within five days after the consummation of a Permitted Acquisition, a written notice in reasonable detail describing such Permitted Acquisition, the reasons why the assets so acquired are within the business described in Schedule 9.6 hereto, specifying the date of the closing of such acquisition and certifying when the Acquisition Period shall begin.

Section 1.3. [Reserved]

Section 1.4. Section 9.6 of the Note Purchase Agreements shall be and is hereby amended in its entirety to read as follows:

Section 9.6. Nature of Business Neither the Company nor any Subsidiary will engage in any business if, as a result, the general nature of the business, taken on a consolidated basis, which would then be engaged in by the Company and its Subsidiaries would be substantially changed from the general nature of the business engaged in by the Company and its Subsidiaries on the date of this Agreement; provided that, notwithstanding the foregoing, the Company may engage in businesses of coal leasing, coal infrastructure (including coal loading and coal handling) and midstream businesses relating to coal and Hydrocarbons (including the managing of coal properties in the United States and the transportation of crude oil and liquid and gaseous hydrocarbons in the United States).

Section 1.5. The following shall be added as new Sections 9.9 and 9.10 of the Note Purchase Agreements:

Section 9.9. Rating Confirmation. No later than March 15 of each year, the Company shall obtain from a Rating Agency a rating of the Notes and provide to each of the holders of the Notes a copy thereof, sent in the manner provided in Section 18 .

Section 9.10. Security by Subsidiaries . The Company will and will cause each Subsidiary that grants a Lien or other security interest pursuant to Section 8.1.13 of the Bank Credit Agreement

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on the assets of the Company, Cantera Natural Gas, LLC or any other Subsidiary to concurrently therewith take, at its sole expense, all such action as shall be necessary to equally and ratably secure the holders of the Notes pursuant to a Lien or other security interest, as applicable, in such assets pari passu with the Lenders pursuant to the Bank Credit Agreement, and within three Business Days thereafter will deliver to each of the holders of the Notes the following items:

(a) an executed security agreement or other necessary and appropriate Lien instrument or instruments (collectively the “Security Documents” ) binding the Company and/or such Subsidiary, as applicable, thereto; and

(b) a certificate signed by the President, a Vice President or another authorized Responsible Officer of the Company and/or such Subsidiary, as applicable, making representations and warranties to the effect of those contained in Sections 5.1, 5.2, 5.6 and 5.7 , but with respect to the Company and/or such Subsidiary, as applicable, and such Security Documents; provided that if representations in scope and form acceptable to the Required Holders are contained in the Security Documents to which the Company and/or such Subsidiary, as applicable, is a party, then such certificate shall not be required; and

(c) such documents and evidence with respect to the Company and/or such Subsidiary, as applicable, as the Required Holders may reasonably request in order to establish the existence and good standing of the Company and/or such Subsidiary, as applicable, and the authorization of the transactions contemplated by such Security Documents as the same pertains to the Company and/or such Subsidiary; and

(d) to the extent delivered pursuant to the Bank Credit Agreement, an opinion of counsel satisfactory to the Required Holders to the effect that such Security Documents have been duly authorized, executed and delivered and constitute the legal, valid and binding contracts and agreements of the Company and/or such Subsidiary, as applicable, enforceable in accordance with their respective terms, except as an enforcement of such terms may be limited by bankruptcy, insolvency, reorganization, moratorium and similar laws affecting the enforcement of creditors’ rights generally and by general equitable principles; and

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(e) an executed counterpart of an intercreditor agreement among the holders of the Notes and each such Person to whom the Company or a Subsidiary, as applicable, is then granting a Lien giving rise to the requirements of this Section 9.10 , which agreement shall provide that the proceeds from the enforcement of any such Lien shall be shared on an equal and ratable basis between and among each such Person and each of the holders of the Notes.

Section 1.6. Section 10.1 of the Note Purchase Agreements shall be and is hereby amended in its entirety to read as follows:

Section 10.1. Limitations on Indebtedness. (a) The Parent Company will not, and will not permit any Subsidiary (including, without limitation, the Company) to, create, issue, assume, guarantee or otherwise incur or in any manner be or become liable in respect of any Indebtedness, except:

(i) Indebtedness evidenced by the Notes;

(ii) Indebtedness of a Wholly-owned Subsidiary to the Parent Company, the Company or another Wholly-owned Subsidiary;

(iii) in addition to the Indebtedness permitted by clauses (i) and (ii) of this Section 10.1(a) , Indebtedness of the Parent Company and its Subsidiaries (including, without limitation, the Company); provided that at the time of creation, issuance, assumption, guarantee or incurrence thereof and after giving effect thereto and to the application of the proceeds thereof:

(1) no Default or Event of Default would exist (including, without limitation, under Section 10.1(e)) ; and

(2) the ratio of Consolidated EBITDA for the four (4) most recently completed Fiscal Quarters, taken as a single accounting period, to Consolidated Interest Expense for the four (4) most recently completed Fiscal Quarters, taken as a single accounting period, would be greater than 3.50 to 1.00;

and provided, further, that notwithstanding the requirements of clause (2) of this Section 10.1(a)(iii) , the Parent Company and its Subsidiaries shall be permitted to create, issue, assume, guaranty or incur Indebtedness pursuant to the Bank Credit Agreement, whether by reason of a draw, borrowing or otherwise, without regard to the limitations of Section 10.1(a)(iii) so long as after

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giving effect to each such draw, borrowing or other incurrence and to the application of the proceeds thereof, the aggregate principal amount of Indebtedness then outstanding pursuant to the Bank Credit Agreement does not exceed $15,000,000 in the aggregate.

(b) The Parent Company will not at any time permit Consolidated Priority Indebtedness to exceed the greater of (i) 15% of Total Partners’ Capital determined as of the end of each Fiscal Quarter of the Parent Company and (ii) $20,000,000.

(c) The renewal, extension or refunding of any Indebtedness, issued, incurred or outstanding pursuant to Section 10.1(a) shall constitute the issuance of additional Indebtedness which is, in turn, subject to the limitations of the applicable provisions of this Section 10.1 .

(d) Any Person which becomes a Subsidiary after the date hereof shall for all purposes of this Section 10.1 be deemed to have created, assumed or incurred at the time it becomes a Subsidiary all Indebtedness of such Person existing immediately after it becomes a Subsidiary.

(e) The Parent Company will not at any time permit the ratio of Consolidated Total Indebtedness to Consolidated EBITDA for the four (4) most recently completed Fiscal Quarters, taken as a single accounting period, to exceed 3.50 to 1.00; provided that in connection with the consummation of a Permitted Acquisition, during the related Acquisition Period, the Parent Company may permit the ratio of Consolidated Total Indebtedness to Consolidated EBITDA for the four (4) most recently completed Fiscal Quarters, taken as a single accounting period, to exceed 3.50 to 1.00, but in no event may such ratio exceed 4.00 to 1.00.

Section 1.7. [Reserved]

Section 1.8. Section 11.1(c) of the Note Purchase Agreements shall be and is hereby amended in its entirety to read as follows:

(c) the Company or the Parent Company, as the case may be, defaults in the performance of or compliance with any term contained in Section 9.9 or Sections 10.1 through 10.6 of this Agreement or Section 6.8 of the Parent Guaranty; or

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Section 1.9. Schedule B of the Note Purchase Agreements shall be amended by amending the following definitions in their respective entirety to read as follows:

“Bank Credit Agreement” means that certain Amended and Restated Credit Agreement dated as of March 3, 2005 by and among the Company, the Guarantors party thereto, the financial institutions party thereto, the Bank Agent, PNC Capital Markets, Inc. and RBC Capital Markets, as joint lead arrangers, and RBC Capital Markets, as syndication agent, a