**Exhibit 99.1**

 

**AMENDED FORM 51-101F2**

**REPORTON RESERVES DATA BY**

**INTERNALQUALIFIED RESERVES EVALUATOR**

** **

Tothe Board of Directors of Nexen Inc. (the “Company”):

 

1.                                       Company staff and I have evaluated the Company’s reserves data as at December 31,2009. The reserves data consist of the following:

 

(a)                                  proved oil and gas reserve quantities estimated as of the last day ofthe Company’s  most recently completedfinancial year using existing economic conditions,

 

(b)                                 the related standardized measure; and

 

(c)                                  probable oil and gas reserve quantities estimated as of the last day ofthe Company’s  most recently completedfinancial year using existing economic conditions.

 

(both (a) and (b) formpart of the “Oil and Gas Reserve Estimation and Disclosures” set out in FASBTopic 932 contained in the Company’s Supplementary Financial Information in itsAnnual Report on Form 10-K).

 

2.                                       The reserves data have been prepared in accordance with:

 

(a)                                  United States’ Securities and Exchange Commission (SEC)requirements;

 

(b)                                 generallyaccepted industry practices in the United States; and

 

(c)                                  thestandards of the Canadian Oil and Gas Evaluation Handbook modified to theextent necessary to reflect SEC requirements.

 

(collectively, the Nexen Reserves Standards).

 

3.                                       The reserves data are the responsibility of the Company’s management. Myresponsibility is to express an opinion whether the evaluation was carried outin accordance with the Nexen Reserves Standards.

 

4.                                       I am not independent of the Company, within the meaning of the term “independent”under National Instrument 51-101.

 

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5.                                       Among other things, with respect to matters regarding royalties,operating costs, development plans and costs, abandonment plans and costs, andincome taxes (where applicable), I have placed reasonable reliance on theinformation and decisions of others in their areas of authority, responsibilityand expertise within the Company.

 

6.                                       In my opinion, the reserves data has, in all material respects, been preparedin accordance with the Nexen Reserves Standards.

 

7.                                       Reserves are estimates only and not exact quantities. Estimates ofeconomically recoverable oil and natural gas reserves and future net cash flowsare based on a number of variable factors, assumptions and judgements regardingfuture events. It is believed that the factors and assumptions used andjudgements made in estimating reserves are reasonable based on the informationavailable at the time the estimates were prepared.  Actual results will vary and such variancescould be material. However, any variations should be consistent with the factthat reserves are categorized according to the probability of their recovery.

 

8.                                       I have no responsibility to update this opinion for events andcircumstances occurring after the date of this opinion.

 

9.                                       I have signed this Form F2 in my capacity as an employee of NexenInc. and not in my personal capacity.

 

 
| /s/ Ian McDonald                          |   |
|-------------------------------------------|--------|
| **Ian McDonald**                          |   |
| **Nexen Inc.**                            |   |
| **Internal Qualified Reserves Evaluator** |   |
| **Calgary, Alberta**                      |   |
|                                      |   |
| **February 17, 2010**                |   |

 

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