Exhibit 15.3





411 N. Sam Houston Parkway
E., Suite 400, Houston, Texas 77060-3545 USA

T +1 281 448 6188 F
+1 281 488 6189 W www.rpsgroup.com



January 31, 2016



CNOOC Limited

No. 25, Chaoyangmenbei Dajie

Dongcheng District

Beijing 100010, P.R. China



Gentlemen:



As per your request, RPS has prepared an
estimate of the proved reserves, future production and income attributable to certain leasehold interests owned by CNOOC Limited
as of December 31, 2015. The reserves and income data were estimated based on the definitions and disclosure guidelines of the
United States Securities and Exchange Commission (SEC) contained in Title 17, Code of Federal Regulations, Modernization of Oil
and Gas Reporting, Final Rule released January 14, 2009 in the Federal Register, including all references to Regulation S-X and
Regulation S-K (SEC regulations). Our third party revision, completed on January 27, 2016 and presented herein, was prepared for
public disclosure by CNOOC Limited in filings made with the SEC in accordance with the disclosure requirements set forth in the
SEC regulations. The estimated reserves and future net income amounts presented in this report, as of December 31, 2015, are based
on the reserve estimate review that RPS performed for PAE’s year-end 2015 reserve report. In our opinion, the assumptions,
data, methods, and procedures used in the preparation of this report are appropriate for such purpose.



CNOOC Limited holds 50% interest in Bridas
Corporation and Bridas Corporation holds 40% interests in PAE. Therefore CNOOC Limited, through Bridas Corporation, owns 20% of
participating interests in PAE.



The subject properties are located in Argentina
and Bolivia, South America. The properties evaluated by RPS account for a portion of CNOOC Limited’s total net proved reserves
as of December 31, 2015.















Based on information provided by CNOOC,
the third party estimate conducted by RPS addresses 5.8 percent of the Total Proved reserves of CNOOC on a barrel oil equivalent
basis (BOE).



The estimated reserves and future net income
amounts presented in this report, as of December 31, 2015, are related to hydrocarbon prices. The hydrocarbon prices used in the
preparation of this report are based on the average prices during the 12-month period prior to the ending date of the period covered
in this report, determined as the unweighted arithmetic averages of the prices in effect on the first-day-of-the-month for each
month within such period, unless prices were defined by regulatory or contractual arrangements, as required by the SEC regulations.
Actual future prices may vary significantly from the prices required by SEC regulations; therefore, volumes of reserves actually
recovered and the amounts of income actually received may differ significantly from the estimated quantities presented in this
report. The results of this study are summarized in the following table.





SEC PARAMETERS

Estimated Net CNOOC Limited Reserves and
Income Data

As of December 31, 2015





Mbbl = Thousand (103) Barrels; MM cf = Million
(106) Cubic Feet











MUS$
= Thousand (103) US Dollars



Note: Hydrocarbon liquids are crude oil,
condensate and gasoline which are reported in thousands (103) stock tank barrels (Mbbl). The Condensate and Gasoline
estimates are volumes captured during field separation and gas plant processing in the field. The natural gas reserves reported
include gas sales and fuel gas. These volumes are reported in million (106) cubic feet (MMcf) at standard conditions
of 14.7 psia and 600Fahrenheit.



In this report, the revenues, deductions
and income data are expressed as thousands of U.S. dollars (M$).



Note: Values by property are shown in Table
1 included in the report.



Note:The future gross revenue is
after the deduction of royalty and turnover taxes in Argentina. The deductions also account for the joint venture (JV) terms PAE
has with Petrominera del Chubut











S.E. (PMC), new JV partner in the Anticlinal
Funes field, in which PAE carries all the investments and cost, in return receives a greater share of the production until reimbursed.
In Bolivia royalty IDH and YPFB part has been also subtracted.



The deductions incorporate the normal direct
costs of operating the wells, recompletion costs, development costs, certain abandonment costs, which are shown as “other”
deductions. The future net income is before the deduction of foreign government income taxes and general administrative overhead,
and has not been adjusted for outstanding loans that may exist, nor does it include any adjustment for cash on hand or undistributed
income.



The discounted future net income shown above
was calculated using a discount rate of 10 percent per annum compounded monthly. Future net income was discounted at four other
discount rates which were also compounded monthly. These results are shown in summary form as follows:







The results shown above are presented for
your information and should not be construed as our estimate of fair market value.



Reserves Included in This Report



The proved reserves included herein conform
to the definition as set forth in the Securities and Exchange Commission’s Rules and Regulations Part 210.4-10(a). An abridged
version of the SEC reserves definitions from Part 210.4-10(a) entitled “Petroleum Reserves Definitions” is included
as an attachment to this report.



The various proved reserve status categories
are defined under the attachment entitled “Petroleum Reserves Definitions” in this report. The proved developed non-producing
reserves included herein consist of the shut-in and behind-pipe categories.



Reserves are “estimated remaining
quantities of oil and gas and related substances anticipated to be economically producible, as of a given date, by application
of development projects to known accumulations.” All reserve estimates involve an assessment of the uncertainty relating
the likelihood that the actual remaining quantities recovered will be greater or less than the estimated quantities determined
as of the date the estimate is made. The uncertainty depends chiefly on the amount of reliable geologic and engineering data available
at the time of the estimate and the











interpretation of these data. The relative
degree of uncertainty may be conveyed by placing reserves into one of two principal classifications, either proved or unproved.
Unproved reserves are less certain to be recovered than proved reserves, and may be further sub-classified as probable and possible
reserves to denote progressively increasing uncertainty in their recoverability. At CNOOC Limited’s request, this report
addresses only the proved reserves attributable to the properties evaluated herein.



Proved reserve estimates will generally
be revised only as additional geologic or engineering data become available or as economic conditions change. For proved reserves,
the SEC states that “as changes due to increased availability of geoscience (geological, geophysical, and geochemical), engineering,
and economic data are made to the estimated ultimate recovery (EUR) with time, reasonably certain EUR is much more likely to increase
or remain constant than to decrease”. Moreover, estimates of proved reserves may be revised as a result of future operations,
effects of regulation by governmental agencies or geopolitical or economic risks. Therefore, the proved reserves included in this
report are estimates only and should not be construed as being exact quantities, and if recovered, the revenues therefrom, and
the actual costs related thereto, could be more or less than the estimated amounts.



For Cerro Dragón, Piedra Clavada
and Koluel Kaike areas there are volumes of Proved Undeveloped Reserves associated with Proved Locations that have been booked
for more than 5 years. PAE's continued development activities over the years have created new opportunities that have delayed drilling
some of the existing Proved locations. All Proved locations are planned to be drilled in the following 5 years in each area.



The proved reserves reported herein are
limited to the period prior to expiration of current contracts providing the legal rights to produce, or a revenue interest in
such production, unless evidence indicates that contract renewal is reasonably certain. Furthermore, properties in the different
countries may be subjected to significantly varying contractual fiscal terms that affect the net revenue to CNOOC Limited for the
production of these volumes. The prices and economic return received for these net volumes can vary significantly based on the
terms of these contracts.



Estimates of Reserves



The estimation of reserves involves two
distinct determinations. The first determination results in the estimation of the quantities of recoverable oil and gas and the
second determination results in the estimation of the uncertainty associated with those estimated quantities in accordance with
the definitions set forth by Part 210.4-10(a). The process of estimating the quantities of recoverable oil and gas reserves relies
on the use of certain generally accepted analytical procedures. These analytical procedures fall into three broad categories or
methods: (1) performance-based methods; (2) volumetric-based methods; and (3) analogy. These methods may be used singularly or
in combination by the reserve evaluator in the process of estimating the quantities of reserves. Reserve evaluators must select
the method or combination of methods which in their professional judgment is most appropriate given the nature and amount of reliable
geoscience and engineering data available at the time of the estimate, the established or anticipated performance











characteristics of the reservoir being evaluated
and the stage of development or producing maturity of the property.



These performance methods include, but may
not be limited to, decline curve analysis and material balance which utilized extrapolations of historical production and pressure
data available through December 31, 2015 in those cases where such data were considered to be definitive. The volumetric method,
analogy or a combination of methods were used where there were inadequate historical performance data to establish a definitive
trend and where the use of production performance data as a basis for the reserve estimates was considered to be inappropriate.
The volumetric analysis utilized pertinent well and seismic data supplied to RPS by PAE that were available through December 31,
2015. The data utilized from the analogues as well as the well and seismic data incorporated into our volumetric analysis were
considered sufficient and appropriate for the purpose thereof.



In many cases, the analysis of the available
geoscience and engineering data and the subsequent interpretation of this data may indicate a range of possible outcomes in an
estimate, irrespective of the method selected by the evaluator. When a range in the quantity of reserves is identified, the evaluator
must determine the uncertainty associated with the incremental quantities of the reserves. Therefore, it is the classification
of reserve quantities as proved, probable and/or possible that addresses the inherent uncertainty in the estimated quantities reported.
All quantities of reserves within the same reserve class must meet the SEC definitions.



To estimate economically recoverable proved
oil and gas reserves and related future net cash flows, we consider many factors and assumptions including, but not limited to,
the use of reservoir parameters derived from geological, geophysical and engineering data that cannot be measured directly, economic
criteria based on current costs and SEC pricing requirements, and forecasts of future production rates.



PAE has made all of the material accounts,
records, geological and other data required for this investigation available to us. In preparing our forecast of future proved
production and income, we have relied upon data furnished by PAE, CNOOC ́s Limited joint venture partner. RPS considers the
factual data used in this report appropriate and sufficient for the purpose of preparing the estimates of reserves and future net
revenues herein.



Estimates of reserves quantities and their
associated reserve class and categories may be revised in the future as additional geoscience or engineering data become available.
Furthermore, estimates of reserves quantities and their associated reserve class and categories may also be revised due to other
factors such as changes in economic conditions, results of future operations, effects of regulation by governmental agencies or
geopolitical or economic risks as previously noted herein.



In summary, we consider the assumptions,
data, methods and analytical procedures used in this report appropriate for the purpose hereof, and we have used all such methods
and procedures that we consider necessary and appropriate to prepare the estimates of reserves herein. The proved reserves included
herein were determined in conformance with SEC regulations. In our opinion,









the proved reserves presented in this report
comply with the definitions, guidelines and disclosure requirements as required by the SEC regulations.



Future Production Rates



For wells currently on production, our forecasts
of future production rates are based on historical performance data. If no production decline trend has been established, future
production rates were held constant, or adjusted for the effects of curtailment where appropriate, until a decline in ability to
produce was anticipated, in which case an estimated rate of decline was then applied to depletion of the reserves. If a decline
trend has been established, this trend was used as the basis for estimating future production rates.



Test data and other related information
were used to estimate the anticipated initial production rates for those wells or locations that are not currently producing. For
reserves not yet on production, sales were estimated to commence at an anticipated date furnished by PAE. Wells or locations that
are not currently producing may start producing earlier or later than anticipated in our estimates due to unforeseen factors causing
a change in the timing to initiate production. Such factors may include delays due to weather, the availability of rigs, the sequence
of drilling, completing and/or recompleting wells and/or constraints set by regulatory bodies.



The future production rates from wells currently
on production or wells or locations that are not currently producing may be more or less than estimated because of changes including,
but not limited to, reservoir performance, operating conditions related to surface facilities, compression and artificial lift,
pipeline capacity and/or operating conditions, producing market demand and/or allowable or other constraints set by regulatory
bodies.



Hydrocarbon Prices



The hydrocarbon prices used herein are based
on SEC price parameters using the average prices during the 12-month period prior to the ending date of the period covered in this
report, determined as the unweighted arithmetic averages of the prices in effect on the first-day-of-the-month for each month within
such period, unless prices were defined by regulatory and contractual arrangements. For hydrocarbon products sold under contract,
the contract prices, including fixed and determinable escalations, exclusive of inflation adjustments, were used until expiration
of the contract. Upon contract expiration, the prices were adjusted to the 12-month unweighted arithmetic average as previously
described.



The product prices that were actually used
to determine the future gross revenue for each property reflect adjustments to the benchmark prices for gravity, quality, local
conditions, gathering and transportation fees and/or distance from market, referred to herein as “differentials.” The
differentials used in the preparation of this report were furnished by PAE and reviewed by RPS for their reasonableness.



Costs



Operating costs for the leases and wells
in this report are based on the operating expense reports of PAE and include only those costs directly applicable to the leases
or wells. The operating costs











include a portion of general and administrative
costs allocated directly to the leases and wells. The operating costs furnished to us were accepted as factual data and reviewed
by us for their reasonableness; however, we have not conducted an independent verification of the operating cost data used by PAE.
No deduction was made for loan repayments, interest expenses or exploration and development prepayments that were not charged directly
to the leases or wells.



Development costs were furnished to us by
PAE and are based on authorizations for expenditure for the proposed work or actual costs for similar projects. The development
costs furnished to us were accepted as factual data and reviewed by us for their reasonableness; however, we have not conducted
an independent verification of these costs. The estimates of the net abandonment costs furnished by PAE were accepted without independent
verification. Current costs used by PAE were held constant throughout the life of the properties.



Standards of Independence and Professional
Qualification



RPS is a multi-disciplinary consultancy,
providing technical, commercial and project management support services in the fields of operations, geoscience, engineering and
health, safety and environment to the energy sector worldwide. RPS’s clients around the world include governments, national
oil companies, integrated majors, independents, and start-ups, legal and financial institutions.



RPS USA is part of the larger UK based RPS
Group plc that employs nearly 5,000 staff based in offices located in the UK, Ireland, the Netherlands, USA, Canada, Australia
and Brazil.



As an independent and experienced consultancy
company with a global capability, RPS is well qualified to provide both technical and economic assessments of reserves/resources,
prospect evaluation, field discoveries and producing fields. In the Oil and Gas Sector, RPS personnel have provided Competent Persons
reports for inclusion in both public and private circulars for funding purposes. We have provided investors with confidential valuations
and assessments during mergers and acquisitions. Asset appraisal and valuation have always been a core element of RPS consulting
business.



As indicated above, this study was based
on data supplied by PAE. The supplied information was reviewed for reasonableness from a technical perspective. As is common in
oil field situations, basic physical measurements taken over time cannot be verified independently in retrospect. As such, beyond
the application of normal professional judgment, such data must be accepted as representative.



The opinions and interpretations presented
in this report represent our best technical interpretation of the data made available to us. However, due to the uncertainty inherent
in the estimation of all sub-surface parameters, we cannot and do not guarantee the accuracy or correctness of any interpretation
and we shall not, except in the case of gross or willful negligence on our part, be liable or responsible for any loss, cost damages
or expenses incurred or sustained by anyone resulting from any interpretation made by any of our officers, agents or employees.











Except for the provision of professional
services on a fee basis, RPS does not have a commercial arrangement with any other person or company involved in the interests
that are the subject of this report.



RPS personnel who prepared this report are
degreed professionals with the appropriate qualifications and experience to complete the estimate work. RPS and its staff do not
claim expertise in accounting, legal and environmental matters, and opinions on such matters do not form part of this report.



Terms of Usage



The results of our third party study, presented
in report form herein, were prepared in accordance with the disclosure requirements set forth in the SEC regulations and intended
for public disclosure as an exhibit in filings made with the SEC by CNOOC Limited.



Very truly yours,



RPS





/S/
Victor Wayne Taylor

Victor Wayne Taylor

PE License# 71417

Principal Engineer