**Exhibit 23.3**

 

**DEGOLYERAND MACNAUGHTON**

5001 SPRING VALLEY ROAD

SUITE 800 EASTDALLAS, TEXAS 75244

 

February 2, 2010

 

NexenInc.

801-7th Avenue S.W.

Calgary,AB 

T2P3P7

 

**Attention: Reserves Review Committee of the Board ofDirectors of Nexen Inc.**

 

**Re:****          ****DeGolyerand MacNaughton - Report of Third Party for certain Yemen properties withinterests owned by Nexen Inc.**

 

Ladiesand Gentlemen:

 

Pursuant to your request, we have conducted anindependent evaluation of Nexen Inc.’s (Nexen) proved and probable oil, condensate,natural gas liquids (NGL), and natural gas reserves, as of December 31,2009, for certain fields owned by Nexen in Yemen as shown in Table 1A. Nexenhas represented that these properties account for 2 percent on an equivalentbarrel basis of its proved reserves as of December 31, 2009, and that itsreserves estimates have been prepared in accordance with the United StatesSecurities and Exchange Commission (SEC) definitions. We have reviewedinformation provided to us by Nexen that it represents to be its estimates ofthe reserves, as of December 31, 2009, for the same properties as thosewhich we evaluated.

 

Reserves included herein are expressed as reservesas represented by Nexen. Gross reserves are defined as the total estimatedpetroleum to be produced from these properties after December 31, 2009.Working interest reserves are defined as that portion of the gross reservesattributable to the interests owned by Nexen after deducting all interestsowned by others. Net reserves are defined as working interest reserves afterdeductions for royalties.

 

Estimates of oil, condensate, and NGL (collectively,Liquids), and natural gas should be regarded only as estimates that may changeas further production history and additional

 

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information become available. Not only are such reserves estimatesbased on that information which is currently available, but such estimates arealso subject to the uncertainties inherent in the application of judgmentalfactors in interpreting such information.

 

Data used in this evaluationwere obtained from reviews with Nexen personnel, Nexen files, from records onfile with the appropriate regulatory agencies, and from public sources. In thepreparation of this report we have relied, without independent verification,upon such information furnished by Nexen with respect to property interests,production from such properties, current costs of operation and development,prices for production, agreements relating to current and future operations andsale of production, and various other information and data that were acceptedas represented. Furthermore, if in the course of our examination something cameto our attention which brought into question the validity or sufficiency of anyof such information or data, we did not rely on such information or data untilwe had satisfactorily resolved our questions relating thereto or hadindependently verified such information or data. A field examination of theproperties was not considered necessary for the purposes of this report.

 

**Methodology and Procedures**

 

The process of estimating reserves requires complexjudgments and decision-making based on available geological, geophysical,engineering, and economic data. To estimate the economically recoverable oiland natural gas reserves and related future net cash flows, we consider manyfactors and make assumptions including:

 

**·****                 **expectedreservoir characteristics based on geological, geophysical, and engineering assessments;

·                   future production ratesbased on historical performance and expected future operating and investmentactivities;

·                   future oil and gas pricesand quality differentials;

·                   assumed effects ofregulation by governmental agencies; and 

·                   future development andoperating costs.

 

Our estimate is preparedusing standard geological and engineering methods generally accepted by thepetroleum industry, and the reserves definitions and standards required by theUnited States SEC. Generally accepted methods for estimating reserves includevolumetric calculations, material balance techniques, production and pressuredecline curve analysis, analogy with similar reservoirs, and reservoirsimulation. The

 

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methodor combination of methods used is based on our professional judgment and experience.

 

Discovered oil and natural gas reserves aregenerally produced only when they are economically recoverable. As such, oiland gas prices and capital and operating costs have an impact on whetherreserves will ultimately be produced. As required by United States SEC rules,reserves represent the quantities that are expected to be economicallyrecoverable using existing prices and costs. Estimates may change substantiallyas additional data from ongoing development activities and production performancebecomes available and as economic conditions impacting oil and gas prices andcosts change.

 

Generally, operations are subject to various levelsof government controls and regulations. These laws and regulations may includematters relating to land tenure, drilling, production practices, environmentalprotection, marketing and pricing policies, royalties, various taxes and leviesincluding income tax, and foreign trade and investment that are subject tochange from time to time. Current legislation is generally a matter of publicrecord, and additional legislation or amendments that will affect reserves orwhen any such proposals, if enacted, might become effective generally cannot bepredicted. Changes in government regulations could affect reserves or relatedeconomics. In the regions that are currently being evaluated, we believe wehave applied existing regulations appropriately.

 

Certain properties in which Nexen has an interestare subject to the terms of various profit sharing or joint operating agreements.The terms of these agreements generally allow for working interest participantsto be reimbursed for portions of capital costs and operating expenses and toshare in the profits. The reimbursements and profit proceeds are converted to abarrel of oil equivalent or standard cubic foot of gas equivalent by dividingby product prices to determine the “entitlement reserves.” These entitlementreserves are equivalent in principle to net reserves and are used to calculatean equivalent net share, termed an “entitlement interest.” In this report,Nexen reserves or interest for certain properties subject to these agreementsis the entitlement based on Nexen’s working interest.

 

**Nexen Estimates**

 

Nexen has represented that its estimated proved andprobable reserves attributable to the evaluated properties are based on UnitedStates SEC definitions. It represents that its estimates of the reservesattributable to these properties represent 2 percent of its total

 

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companyproved reserves and less than 1 percent of its total company probable reserveson an equivalent barrel basis and are as follows, expressed in thousands ofbarrels (mbbl), millions of cubic feet (mmcf) and thousands of barrels of oilequivalent (mboe):

 

**Nexen’sestimate of Reserves as of December 31, 2009**

**SelectFields Evaluated by DeGolyer and MacNaughton**

 

**YemenProperties**

 
| ** **                                       | ** ** | **Liquids** | ** ** | **Natural Gas** | ** ** | **Oil Equivalent** | ** ** |
|--------------------------------------------------|------------|-------------|------------|----------------------|------------|-------------------------|------------|
| **Nexen Reserves**                          | ** ** | **(mbbl)**  | ** ** | **(mmcf)**           | ** ** | **(mboe)**              | ** ** |
| **Working Interest Reserves (before royalties)** |       |        |       |                 |       |                    |       |
| **Proved**                                       |       | 21,195      |       | 0                    |       | 21,195                  |       |
| **Probable**                                     |       | 2,575       |       | 0                    |       | 2,575                   |       |
| **Working Interest Reserves (after royalties)**  |       |        |       |                 |       |                    |       |
| **Proved**                                       |       | 13,258      |       | 0                    |       | 13,258                  |       |
| **Probable**                                     |       | 1,258       |       | 0                    |       | 1,258                   |       |

 

Note:  Gas is converted to oil equivalent using a factor of6,000 cubic feet of gas per 1 barrel of oil equivalent.

 

**Reserves Audit Opinion**

 

DeGolyer and MacNaughton has used all procedures andmethods that it considers necessary to prepare this report.

 

In our opinion, the information relating toestimated net proved and net probable reserves of oil, condensate, natural gasliquids, and gas contained in this report has been prepared according to thedefinitions and disclosure guidelines required by the United States SEC withinParagraphs 932-235-50-4, 932-235-50-6, 932-235-50-7, and 932-235-50-9 of theAccounting Standards Update 932-235-50, Extractive Industries — Oil and Gas(Topic 932): Oil and Gas Reserve Estimation and Disclosures (January 2010)of the Financial Accounting Standards Board and Rules 4—10(a) (1)—(32)of Regulation S—X and Rules 302(b), 1201, and 1202(a) (1), (2), (3),(4), (5), (8) of Regulation S—K of the United States Securities andExchange Commission.

 

In comparing the detailed proved andproved-plus-probable reserves estimates prepared by us to those prepared byNexen, we have found differences, both positive and negative. In our opinion,the proved and proved-plus-probable reserves for the reviewed properties asestimated by Nexen are, in aggregate when compared to our estimates on thebasis of equivalent barrels, reasonable within the established audit toleranceguidelines as

 

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setforth in the Standards Pertaining to the Estimating and Auditing of Oil and GasReserves Information promulgated by the Society of Petroleum Engineers.

 

DeGolyer and MacNaughton is an independent petroleumengineering consulting firm that has been providing petroleum consultingservices throughout the world for over 70 years. DeGolyer and MacNaughton doesnot have any financial interest, including stock ownership, in Nexen. Our feeswere not contingent on the results of our evaluation. This letter report hasbeen prepared at the request of Nexen and should not be used for purposes otherthan those for which it is intended.

 
|   |                           | Submitted,                               |
|--------|--------------------------------|------------------------------------------|
|   |                           |                                     |
|   |                           | /s/  DeGolyer and MacNaughton            |
|   |                           |                                     |
|   |                           | DeGOLYER  and MacNAUGHTON                |
|   |                           | Texas  Registered Engineering Firm F-716 |
|   |                           |                                     |
|   |                           |                                     |
| cc:    | Mr. Craig  Beattie        |                                     |   |
|   | V. P. Technical Assurance      |                                     |   |
|   | Nexen International Division   |                                     |   |
|   | Mr. Brad  Kopas           |                                     |   |
|   | Deloitte & Touche LLP |                                     |   |
|   |                           |                                     |   |
|   |                           |                                     |   |
| [SEAL] |                           | /s/  Lloyd W. Cade, P.E.                 |
|   |                           |                                     |
|   |                           | Lloyd  W. Cade, P.E.                     |
|   |                           | Senior  Vice President                   |
|   |                           | DeGolyer  and MacNaughton                |

 

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**TABLE 1A**

**NEXENFIELDS EVALUATED by DeGOLYER and MacNAUGHTON**

**as of**

**DECEMBER31, 2009**

 

| **PROPERTIES**           | ** ** | **FIELDS**         |
|--------------------------|------------|--------------------|
|                     |       |               |
| Yemen  Masila (Block 14) |       | Bainoon/Naziah     |
|                     |       | Camaal             |
|                     |       | Dahban             |
|                     |       | Dais               |
|                     |       | Haru               |
|                     |       | Heijah             |
|                     |       | Hemiar             |
|                     |       | Naar               |
|                     |       | North  East Camaal |
|                     |       | North  Camaal      |
|                     |       | North  East Sunah  |
|                     |       | Qataban            |
|                     |       | Raydah             |
|                     |       | Ressib             |
|                     |       | South  Hemiar      |
|                     |       | South  Ressib      |
|                     |       | Sunah              |
|                     |       | Tawila             |
|                     |       | West  Camaal       |
|                     |       | West  Hemiar       |

 

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