Exhibit 15.5
















January 20, 2017



CNOOC
Limited



c/o Nexen
Energy ULC



801 –
7th Avenue SW



Calgary,
Alberta



T2P 3P7



| | Re: | McDaniel
                                         & Associates - Report of Third Party for certain Canadian Oil Sands properties owned
                                         by CNOOC Limited
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



Gentlemen:



Pursuant
to your request, McDaniel & Associates Consultants Ltd. (“McDaniel”) has conducted an independent audit of CNOOC
Limited’s (“CNOOC”) proved synthetic crude oil reserves, as of December 31, 2016, for certain Canadian Oil Sands properties owned by CNOOC and managed by its wholly-owned subsidiary, Nexen
Energy ULC (“Nexen”), as shown in Table 1. CNOOC has represented that these properties account for eight percent of
its total company proved reserves on an equivalent barrel basis as of December 31, 2016, and that its reserves estimates have
been prepared in accordance with the United States Securities and Exchange Commission (SEC) definitions. We have reviewed information
provided to us by Nexen on behalf of CNOOC that it represents to be to be its estimates of the reserves, as of December 31, 2016,
for the same properties as those which we audited. The completion date of our report is January 20, 2017. This report was prepared
in accordance with guidelines specified in Item 1202(a)(8) of Regulation S-K and is to be used for inclusion in certain filings of the SEC.



Reserves
included herein are expressed as reserves as represented by CNOOC. Gross reserves are defined as the total estimated petroleum
to be produced from these properties after December 31, 2016. Working interest reserves are defined as that portion of the gross
reserves attributable to the interests owned by CNOOC after deducting all working interests owned by others. Net reserves are
defined as working interest reserves after the deduction of royalties.



Estimates
of synthetic crude oil should be regarded only as estimates that may change as further production history and additional information
become available. Not only are such reserves estimates based on that information which is currently available, but such estimates
are also subject to the uncertainties inherent in the application of judgmental factors in interpreting such information.











2200, Bow Valley Square 3, 255 - 5 Avenue
SW, Calgary AB T2P 3G6 Tel: (403) 262-5506 Fax: (403) 233-2744 www.mcdan.com








Nexen Energy ULCJanuary 20, 2017Report of Third Party for certain Canadian Oil Sands Property owned by CNOOC LimitedPage 2




Data used
in this audit were obtained from reviews with Nexen personnel, Nexen files, from records on file with the appropriate regulatory
agencies, and from public sources. In the preparation 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 and sale of production, and various
other information and data that were accepted as represented. Furthermore, if in the course of our examination something came
to our attention, which brought into question the validity or sufficiency of any of such information or data, we did not rely
on such information or data until we had satisfactorily resolved our questions relating thereto or had independently verified
such information or data. A field examination of the properties was not considered necessary for the purposes of this report.



Methodology
and Procedures



The process
of estimating reserves requires complex judgments and decision-making based on available geological, geophysical, engineering
and economic data. To estimate the economically recoverable oil, synthetic crude oil and natural gas reserves, and related future
net cash flows, we consider many factors and make assumptions including:





| | · | expected
                                         reservoir characteristics based on geological, geophysical and engineering assessments;
| | - | -----------------------------------------------------------------------------------------------------------------------------------------



| | · | future
                                         production rates based on historical performance and expected future operating and investment
                                         activities;
| | - | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | · | future
                                         oil and gas prices and quality differentials;
| | - | ---------------------------------------------------------------------------------------------



| | · | assumed
                                         effects of regulation by governmental agencies; and
| | - | ----------------------------------------------------------------------------------------------------



| | · | future
                                         development and operating costs
| | - | -------------------------------------------------------------------------------





Estimates
of reserves were prepared using standard geological and engineering methods generally accepted by the petroleum industry as presented
in the publication of the Society of Petroleum Engineers entitled “Standards Pertaining to the Estimating and Auditing of
Oil and Gas Reserves Information (Revision as of February 19, 2007).” Generally accepted methods for estimating reserves
include volumetric calculations, material balance techniques, production decline curves, pressure transient analysis, analogy
with similar reservoirs, and reservoir simulation. The method or combination of methods used is based on professional judgment
and experience.



Discovered
oil and natural gas reserves are generally only produced when they are economically recoverable. As such, oil and gas prices,
and capital and operating costs have an impact on whether reserves will ultimately be produced. As required by SEC rules, reserves
represent the quantities that are expected to be economically recoverable using existing prices and costs. Estimates may change
substantially as additional data from ongoing development activities and production performance becomes available and as economic
conditions impacting oil and gas prices and costs change.






Nexen Energy ULCJanuary 20, 2017Report of Third Party for certain Canadian Oil Sands Property owned by CNOOC LimitedPage 3




The proved
reserves estimates in this report were based upon 2016 first-of-the month fiscal average pricing using benchmark pricing. Oil
prices were primarily based upon West Texas Intermediate at Cushing crude oil benchmark of US$42.75 per barrel. Specific pricing
for each field was adjusted for historical quality and transportation cost differentials, and for currency exchange rates. The
resulting adjusted price is referred to as the “realized price.” For total proved reserves, the estimated realized
prices were US$43.46 per barrel of synthetic crude oil for the Syncrude property evaluated.



Generally,
operations are subject to various levels of government controls and regulations. These laws and regulations may include matters
relating to land tenure, drilling, production practices, environmental protection, marketing and pricing policies, royalties,
various taxes and levies including income tax, and foreign trade and investment, that are subject to change from time to time.
Current legislation is generally a matter of public record, and additional legislation or amendments that will affect reserves
or when any such proposals, if enacted, might become effective generally cannot be predicted. Changes in government regulations
could affect reserves or related economics. In the regions that are currently being evaluated we believe we have applied existing
regulations appropriately.



CNOOC
Estimates



Nexen on
behalf of CNOOC has represented that estimated proved reserves attributable to the property audit are based on SEC definitions.
CNOOC represents that its estimates of the reserves attributable to this property represent eight percent of its total company
proved reserves after royalties on an equivalent basis and are as follows, expressed in thousands of barrels (Mbbl), and thousands
of barrels of oil equivalent (Mboe):



CNOOC’s
estimate of Reserves as of December 31, 2016



Canadian
Oil Sands Property Audited by McDaniel & Associates



Syncrude



|CNOOC
    Reserves                              | Synthetic
        Crude Oil
        
        (Mbbl) | Oil
    Equivalent (Mboe)
|----------------------------------------------- | --------------------------------------------------- | -------------------------
|Working
    Interest Reserves (after royalties)
|Proved                                          | 300,503                                             | 300,503                  



Note: Gas
is converted to oil equivalent using a factor of 6,000 cubic feet of gas per 1 barrel of oil equivalent based on an energy equivalent
basis.



Reserves
Audit Opinion



McDaniel
has used all data, assumptions, procedures and methods that it considers necessary to prepare this report.






Nexen Energy ULCJanuary 20, 2017Report of Third Party for certain Canadian Oil Sands Property owned by CNOOC LimitedPage 4




In our opinion,
the information relating to estimated proved reserves of synthetic crude oil contained in this opinion has been prepared in accordance
with Paragraphs 932-235-50-4, 932-235-50-6, 932-235-50-7 and 932-235-50-9 of the Accounting 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 Securities and Exchange Commission.



We have
examined the assumptions, data, methods procedures and proved reserves estimates prepared by Nexen on behalf of CNOOC. In our
opinion, the proved reserves for the reviewed properties as estimated by CNOOC are, in aggregate on the basis of equivalent barrels,
reasonable because when compared to our estimates, or if we were to perform our own detailed estimates, reflect a difference of
not more than plus or minus 10 percent.



The analyses
of this property, as reported herein, were conducted within the context of an audit of a distinct group of properties in aggregate
as part of the total corporate level reserves. Extraction and use of these analyses outside of this context may not be appropriate
without supplementary due diligence.



McDaniel
is an independent petroleum engineering consulting firm that has been providing petroleum consulting services throughout the world
for over 60 years. McDaniel does not have any financial interest, including stock ownership, in CNOOC. Our fees were not contingent
on the results of our evaluation. This letter report has been prepared at the request of Nexen on behalf of CNOOC.



This report
was prepared by McDaniel & Associates Consultants Ltd. for the exclusive use of CNOOC. It is not to be reproduced, distributed,
or made available, in whole or in part to any person, company, or organization other than CNOOC without the knowledge and consent
of McDaniel & Associates Consultants Ltd. We reserve the right to revise any of the estimates provided herein if any relevant
data existing prior to preparation of this report was not made available or if any data provided was found to be erroneous.



If there
are any questions, please contact the writer directly at (403) 218-1379.



Sincerely,



McDaniel & Associates
Consultants Ltd.







/s/ P. A. Welch

____________________________



P. A. Welch, P. Eng.











|CC: | Mr. Scott Chalker, GM – JV & OS Commercial,
    Cdn Ops, Canadian Operations & OOGC
|--- | -----------------------------------------------------------------------------------
|    | Ms. Charishe Amante, P. Eng., Corporate Reserves
    Analyst                       
|    | Terrance Kryschuk, Deloitte LLP                                                    
|    | Jenny Yang, Deloitte LLP                                                           








Nexen Energy ULCJanuary 20, 2017Report of Third Party for certain Canadian Oil Sands Property owned by CNOOC LimitedPage 5




Table
1



CNOOC
Properties Audited by McDaniel & Associates



Select
Canadian Oil Sands Properties



December
31, 2016



| | BUSINESS
    UNIT | FIELD
    NAME
| | ----------------- | --------------
| |                   |               
| | OIL SANDS         | SYNCRUDE      












Nexen Energy ULCJanuary 20, 2017Report of Third Party for certain Canadian Oil Sands Property owned by CNOOC LimitedPage 6




CERTIFICATE
OF QUALIFICATION



I, Philip
Arthur Welch, Petroleum Engineer of 2200, 255 - 5th Avenue, S.W., Calgary, Alberta, Canada hereby certify:



| | 1. | That I
                                         am the President & Managing Director of McDaniel & Associates Consultants Ltd.,
                                         APEGA Permit Number P3145, which Company did prepare, at the request of CNOOC Limited.,
                                         the report entitled "Report of Third Party for certain Canadian Oil Sands property
                                         owned by CNOOC Limited, As of December 31, 2016", dated January 20, 2017, and that
                                         I supervised the preparation of this report.
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 2. | That I
                                         attended the University of British Columbia in the years 1980 to 1987 and that I graduated
                                         with a Bachelor of Applied Science and Master of Applied Science degrees in Mechanical
                                         Engineering, that I am a registered Professional Engineer with the Association of Professional
                                         Engineers and Geoscientists of Alberta; that I am a member of the Society of Petroleum
                                         Engineers; that I am a member of the Society of Petroleum Evaluation Engineers; and that
                                         I have in excess of 25 years of experience in oil and gas reservoir studies and evaluations.
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 3. | That I
                                         have no direct or indirect interest in the properties or securities of CNOOC Limited.,
                                         nor do I expect to receive any direct or indirect interest in the properties or securities
                                         of CNOOC Limited., or any affiliate thereof.
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 4. | That the
                                         aforementioned report was not based on a personal field examination of the properties
                                         in question, however, such an examination was not deemed necessary in view of the extent
                                         and accuracy of the information available on the properties in question.
| | -- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------







/s/ P. A.
Welch



____________________________



P. A. Welch,
P. Eng.



Calgary,
Alberta



Dated: January
20, 2017