Exhibit
99.3




DeGolyer
and MacNaughton


5001
Spring Valley Road


Suite 800
East


Dallas,
Texas 75244





June 24,
2010




Board of
Directors


Ecopetrol
S.A.


Calle 35
No. 7-21 Piso 1


Bogota,
D.C. Colombia




Gentlemen:




Pursuant
to your request, we have conducted a reserves evaluation of the net proved crude
oil, condensate, and natural gas reserves, as of December 31, 2009, the
effective date of this report, of certain selected properties in North America
and South America owned by Ecopetrol S.A. (ECOPETROL). ECOPETROL has represented
that these properties account for 50 percent on a net equivalent barrel basis of
ECOPETROL’s net proved reserves as of December 31, 2009. The net proved reserves
estimates prepared by us have been prepared in accordance with the reserves
definitions of Rules 4–10(a) (1)–(32) of Regulation S–X of the Securities and
Exchange Commission (SEC) of the United States. Our reserves evaluation was
completed on January 21, 2010.





Reserves
included herein are expressed as net reserves. Gross reserves are defined as the
total estimated petroleum to be produced from these properties after December
31, 2009. Net reserves are defined as that portion of the gross reserves
attributable to the interests owned by ECOPETROL after deducting all interests
owned by others.





Estimates
of oil, condensate, and natural gas 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.










DeGolyer
and MacNaughton





Data used
in this evaluation were obtained from reviews with ECOPETROL personnel, and from
ECOPETROL files. In the preparation of this report we have relied, without
independent verification, upon such information furnished by ECOPETROL with
respect to property interests, production from such properties, current costs of
operation and development, current 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. A field examination of
the properties was not considered necessary for the purposes of this report. We
believe the data used in this evaluation are appropriate for the purposes of
this report.





Methodology and
Procedures




Estimates
of reserves were prepared by the use of standard geological and engineering
methods generally accepted by the petroleum industry. The method or combination
of methods used in the analysis of each reservoir was tempered by experience
with similar reservoirs, stage of development, quality and completeness of basic
data, and production history.





When
applicable, the volumetric method was used to estimate the original oil in place
(OOIP) and the original gas in place (OGIP). Structure and isopach maps were
constructed to estimate reservoir volume. Electrical logs, radioactivity logs,
core analyses, and other available data were used to prepare these maps as well
as to estimate representative values for porosity and water saturation. When
adequate data were available and when circumstances justified, material balance
and other engineering methods were used to estimate OOIP or OGIP.





Estimates
of ultimate recovery were obtained after applying recovery factors to OOIP or
OGIP. These recovery factors were based on consideration of the type of energy
inherent in the reservoirs, analyses of the petroleum, the structural positions
of the properties, and the production histories. When applicable, material
balance and other engineering methods were used to estimate recovery factors. An
analysis of reservoir performance, including production rate, reservoir
pressure, and gas-oil ratio behavior, was used in the estimation of
reserves.





For
depletion-type reservoirs or those whose performance disclosed a reliable
decline in producing-rate trends or other diagnostic characteristics, reserves
were estimated by the application of appropriate decline curves or other
performance relationships. In the analyses of production-decline curves,
reserves were estimated only to the limits of economic production or to the
limit of the production licenses as appropriate. We believe these methods are
appropriate for the purposes of this report.










DeGolyer
and MacNaughton





Definition of
Reserves




Petroleum
reserves estimated by us included in this report are classified by degree of
proof as proved and are judged to be economically producible in future years
from known reservoirs under existing economic and operating conditions and
assuming continuation of current regulatory practices using conventional
production methods and equipment. In the analyses of production-decline curves,
reserves were estimated only to the limit of economic rates of production under
existing economic and operating conditions using prices and costs consistent
with the effective date of this report, including consideration of changes in
existing prices provided only by contractual arrangements but not including
escalations based upon future conditions. Proved reserves classifications used
by us in this report are in accordance with the reserves definitions of Rules
4–10(a) (1)–(32) of Regulation S–X of the SEC. The petroleum reserves are
classified as follows:





Proved oil and gas reserves –
Proved oil and gas reserves are those quantities of oil and gas, which, by
analysis of geoscience and engineering data, can be estimated with reasonable
certainty to be economically producible—from a given date forward, from known
reservoirs, and under existing economic conditions, operating methods, and
government regulations—prior to the time at which contracts providing the right
to operate expire, unless evidence indicates that renewal is reasonably certain,
regardless of whether deterministic or probabilistic methods are used for the
estimation. The project to extract the hydrocarbons must have commenced or the
operator must be reasonably certain that it will commence the project within a
reasonable time.





(i) The
area of the reservoir considered as proved includes:


(A) The
area identified by drilling and limited by fluid contacts, if any, and (B)
Adjacent undrilled portions of the reservoir that can, with reasonable
certainty, be judged to be continuous with it and to contain economically
producible oil or gas on the basis of available geoscience and engineering
data.










DeGolyer
and MacNaughton





(ii) In
the absence of data on fluid contacts, proved quantities in a reservoir are
limited by the lowest known hydrocarbons (LKH) as seen in a well penetration
unless geoscience, engineering, or performance data and reliable technology
establishes a lower contact with reasonable certainty.





(iii)
Where direct observation from well penetrations has defined a highest known oil
(HKO) elevation and the potential exists for an associated gas cap, proved oil
reserves may be assigned in the structurally higher portions of the reservoir
only if geoscience, engineering, or performance data and reliable technology
establish the higher contact with reasonable certainty.





(iv)
Reserves which can be produced economically through application of improved
recovery techniques (including, but not limited to, fluid injection) are
included in the proved classification when:


(A)
Successful testing by a pilot project in an area of the reservoir with
properties no more favorable than in the reservoir as a whole, the operation of
an installed program in the reservoir or an analogous reservoir, or other
evidence using reliable technology establishes the reasonable certainty of the
engineering analysis on which the project or program was based; and (B) The
project has been approved for development by all necessary parties and entities,
including governmental entities.





(v)
Existing economic conditions include prices and costs at which economic
producibility from a reservoir is to be determined. The price shall be the
average price during the 12-month period prior to the ending date of the period
covered by the report, determined as an unweighted arithmetic average of the
first-day-of-the-month price for each month within such period, unless prices
are defined by contractual arrangements, excluding escalations based upon future
conditions.





Developed oil and gas
reserves – Developed oil and gas reserves are reserves of any category
that can be expected to be recovered:










DeGolyer
and MacNaughton





(i)
Through existing wells with existing equipment and operating methods or in which
the cost of the required equipment is relatively minor compared to the cost of a
new well; and





(ii)
Through installed extraction equipment and infrastructure operational
at the time of the reserves estimate if the extraction is by means not
involving a well.





Undeveloped reserves –Undeveloped oil and gas reserves are reserves of any category that are
expected to be recovered from new wells on undrilled acreage, or from existing
wells where a relatively major expenditure is required for
recompletion.





(i)
Reserves on undrilled acreage shall be limited to those directly offsetting
development spacing areas that are reasonably certain of production when
drilled, unless evidence using reliable technology exists that establishes
reasonable certainty of economic producibility at greater
distances.





(ii)
Undrilled locations can be classified as having undeveloped reserves only if a
development plan has been adopted indicating that they are scheduled to be
drilled within five years, unless the specific circumstances, justify a longer
time.





(iii)
Under no circumstances shall estimates for undeveloped reserves be attributable
to any acreage for which an application of fluid injection or other improved
recovery technique is contemplated, unless such techniques have been proved
effective by actual projects in the same reservoir or an analogous reservoir, as
defined in section 210.4–10 (a) Definitions, or by other evidence using reliable
technology establishing reasonable certainty.




Primary Economic
Assumptions




The
following economic assumptions were used for estimating existing and future
prices and costs:





6




DeGolyer
and MacNaughton




Oil
and Condensate Prices




ECOPETROL
has represented that the oil and condensate prices were based on a 12-month
average price (reference price), calculated as the unweighted arithmetic
average of the first-day-of-the-month price for each month within the 12-month
period prior to the end of the reporting period, unless prices are defined by
contractual arrangements. ECOPETROL supplied differentials by field to a
Brent reference price and the prices were held constant
thereafter.




Natural
Gas Prices




ECOPETROL
has represented that the natural gas prices were based on a reference price,
calculated as the unweighted arithmetic average of the first-day-of-the-month
price for each month within the 12-month period prior to the end of the
reporting period, unless prices are defined by contractual arrangements based on
specific market segments.




Operating
Expenses and Capital Costs




Operating
expenses and capital costs, based on information provided by ECOPETROL, were
used in estimating future costs required to operate the properties. In certain
cases, future costs, either higher or lower than existing costs, may have been
used because of anticipated changes in operating conditions. These costs were
not escalated for inflation.





While the
oil and gas industry may be subject to regulatory changes from time to time that
could affect an industry participant’s ability to recover its oil and gas
reserves, we are not aware of any such governmental actions which would restrict
the recovery of the December 31, 2009, estimated oil and gas volumes. The
reserves estimated in this report can be produced under current regulatory
guidelines.





Our
estimates of ECOPETROL’s net proved reserves attributable to the reviewed
properties are based on the definitions of proved reserves of the SEC and are as
follows, expressed in thousands of barrels (Mbbl), millions of cubic feet
(MMcf), and thousands of barrels of oil equivalent (Mboe):










DeGolyer
and MacNaughton





Net Proved Reserves
                                      as of
                                      December 31, 2009Oil and
                                      Condensate
                                      (MMbbl)
                                    
                                    
                                    Natural
                                      Gas
                                      (MMcf)
                                    
                                    
                                    Oil
                                      Equivalent
                                      (MMboe)North
      AmericaProved
      Developed
                                    
                                    
                                    4,651
                                    
                                    
                                    
                                    2,576
                                    
                                    
                                    
                                    5,110Proved
      Undeveloped
                                    
                                    
                                    0
                                    
                                    
                                    
                                    0
                                    
                                    
                                    
                                    0North
      America Total Proved
                                    
                                    
                                    4,651
                                    
                                    
                                    
                                    2,576
                                    
                                    
                                    
                                    5,110South
      AmericaProved
      Developed
                                    
                                    
                                    152,187
                                    
                                    
                                    
                                    1,683,313
                                    
                                    
                                    
                                    451,976Proved
      Undeveloped
                                    
                                    
                                    206,697
                                    
                                    
                                    
                                    586,497
                                    
                                    
                                    
                                    311,149South
      America Total Proved
                                    
                                    
                                    358,884
                                    
                                    
                                    
                                    2,269,810
                                    
                                    
                                    
                                    763,125Total
      Proved
                                    
                                    
                                    363,535
                                    
                                    
                                    
                                    2,272,386
                                    
                                    
                                    
                                    768,235Note:
      Gas is converted to oil equivalent using a factor of 5,615 cubic feet of
      gas per 1 barrel of oil equivalent.





The
assumptions, data, methods, and procedures used by DeGolyer and MacNaughton to
conduct the reserves evaluation are appropriate for purposes of this
report.





In our
opinion, the information relating to estimated proved reserves of oil,
condensate, natural gas liquids, and gas contained in this report 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, 1202(a) (1), (2), (3), (4), (8), and
1203(a) of Regulation S–K of the Securities and Exchange
Commission.





To the
extent the above-enumerated rules, regulations, and statements require
determinations of an accounting or legal nature, we are necessarily unable to
express an opinion as to whether the above-described information is in
accordance therewith or sufficient therefor.





8




DeGolyer
and MacNaughton





DeGolyer
and MacNaughton is an independent petroleum engineering consulting firm that has
been providing petroleum consulting services throughout the world for over 70
years. DeGolyer and MacNaughton does not have any financial interest, including
stock ownership, in ECOPETROL. Our fees were not contingent on the results of
our evaluation. This letter report has been prepared at the request of
ECOPETROL.




Submitted,DeGOLYER
      and MacNAUGHTONTexas
      Registered Engineering Firm
F-716





/s/
      R. M. Shuck, P.E.R.
      M. Shuck, P.E.Senior
      Vice PresidentDeGolyer
      and MacNaughton





DeGolyer
and MacNaughton




CERTIFICATE of
QUALIFICATION




I, R.
Michael Shuck, Petroleum Engineer with DeGolyer and MacNaughton, 5001 Spring
Valley Road, Suite 800 East, Dallas, Texas, 75244 U.S.A., hereby
certify:





1.
            That
      I am a Senior Vice President with DeGolyer and MacNaughton, which company
      did prepare the letter report addressed to ECOPETROL dated June 24,
      2010, and that I, as Senior Vice President, was responsible for the
      preparation of this report.





2.
            That
      I attended University of Houston, and that I graduated with a Bachelor of
      Science degree in Chemical Engineering in the year 1977; that I am a
      Registered Professional Engineer in the State of Texas; that I am a
      member of the International Society of Petroleum Engineers; and that I
      have in excess of 32 years of experience in the oil and gas reservoir
      studies and reserves evaluations.





SIGNED:
June 24, 2010





/s/
      R. M. ShuckR.
      M. Shuck, P.E.Senior
      Vice PresidentDeGolyer
      and MacNaughton