Exhibit 99.4

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January 27, 2011

Mr. Aquiles Rattia

Repsol YPF

Paseo de Castellana 278, 011b

Madrid 28006

Spain

Dear Mr. Rattia:

In accordance with your request, we have estimated the proved reserves, as of December 31, 2009, to the Repsol YPF (Repsol) interest in certain oil and gas properties located in Shenzi Field, deepwater
Gulf of Mexico. We completed our evaluation on January 31, 2010. It is our understanding that the proved reserves estimated in this report constitute approximately 3.3 percent of all proved reserves owned by Repsol; it is also our understanding
that the proved undeveloped reserves estimated in this report constitute approximately 6.1 percent of all proved undeveloped reserves owned by Repsol. Economic analysis was performed only to confirm commercial viability and determine economic limits
for the properties, using the price and cost parameters discussed in subsequent paragraphs of this letter. The estimates in this report have been prepared in accordance with the definitions and guidelines of the U.S. Securities and Exchange
Commission (SEC) and conform to the FASB Accounting Standards Codification Topic 932, Extractive ActivitiesOil and Gas. Definitions are presented immediately following this letter. This report has been prepared for Repsols use in filing
with the SEC.

We estimate the gross (100 percent) reserves and net reserves to the Repsol interest in these properties, as of December 31,
2009, to be:



|         |  |                     |  |                  |  |               |  |                 
|-------- |  | ------------------- |  | ---------------- |  | ------------- |  | ----------------
|         |  | Reserves           
|         |  | Gross (100 Percent) |  | Net             
|Category |  | Oil    (MBBL)       |  | Sales Gas (MMCF) |  | Oil    (MBBL) |  | Sales Gas (MMCF)
|         |  |                     |  |                 
|Proved   |  | 249,395             |  | 44,324           |  | 66,987        |  | 11,896          

The oil reserves shown
include crude oil only. Oil volumes are expressed in thousands of barrels (MBBL); a barrel is equivalent to 42 United States gallons. Sales gas volumes are expressed in millions of cubic feet (MMCF) at standard temperature and pressure bases.

The estimates shown in this report are for proved reserves. As requested, probable and possible reserves that exist for these
properties have not been included. Reserves categorization conveys the relative degree of certainty; reserves subcategorization is based on development and production status. The estimates of reserves included herein have not been adjusted for risk.

For the purposes of this report, we did not perform any field inspection of the properties, nor did we examine the mechanical
operation or condition of the wells and facilities. We have not investigated possible environmental liability related to the properties.





|                                                                                                            |  |  |                      | 
|----------------------------------------------------------------------------------------------------------- |  |  | -------------------- | 
|4500 THANKSGIVING TOWER  1601 ELM STREET - DALLAS,
TEXAS 75201-4754  PH: 214-969-5401  FAX: 214-969-5411 |  |  | nsai@nsai-petro.com  | 
|1221 LAMAR STREET, SUITE 1200  HOUSTON, TEXAS
77010-3072  PH: 713-654-4950  FAX: 713-654-4951            |  |  | netherlandsewell.com | 



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Oil and gas prices were used only to confirm commercial viability and determine economic
limits for the properties. Prices used in this report are based on the 12-month unweighted arithmetic average of the first-day-of-the-month price for each month for the period January through December 2009. For oil volumes, the average West Texas
Intermediate posted price of $57.65 per barrel is adjusted by lease for quality and a regional price differential. For gas volumes, the average Henry Hub spot price used is $3.866 per MMBTU. All prices are held constant throughout the lives of the
properties. The average adjusted oil and gas prices of $56.06 per barrel and $4.190 per MMBTU are held constant throughout the lives of the properties.

Operating costs and capital costs were used only to confirm commercial viability and determine economic limits for the properties. Lease and well operating costs used in this report are based on the Repsol
plan of development for Shenzi Field. These costs include estimates of costs to be incurred at and below the district and field levels as well as headquarters general and administrative overhead expenses of Repsol. As requested, lease and well
operating costs are held constant throughout the lives of the properties. Capital costs are included as required for new development wells and production equipment. The future capital costs are held constant to the date of expenditure.

The reserves shown in this report are estimates only and should not be construed as exact quantities. Proved reserves are those quantities
of oil and gas which, by analysis of engineering and geoscience data, can be estimated with reasonable certainty to be economically producible. Estimates of reserves may increase or decrease as a result of market conditions, future operations,
changes in regulations, or actual reservoir performance. In addition to the primary economic assumptions discussed herein, our estimates are based on certain assumptions including, but not limited to, that the properties will be developed consistent
with current development plans, that the properties will be operated in a prudent manner, that no governmental regulations or controls will be put in place that would impact the ability of Repsol to recover the reserves, and that our projections of
future production will prove consistent with actual performance. If the reserves are recovered, the revenues therefrom and the costs related thereto could be more or less than the estimated amounts used to determine economic limits and commercial
viability of such reserves. Because of governmental policies and uncertainties of supply and demand, the sales rates, prices received for the reserves, and costs incurred in recovering such reserves may vary from assumptions made while preparing
this report.

For the purposes of this report, we used technical and economic data including, but not limited to, well logs,
geologic maps, seismic data, well test data, production data, historical price and cost information, and property ownership interests. The reserves in this report have been estimated using deterministic methods; these estimates have been prepared in
accordance with the Standards Pertaining to the Estimating and Auditing of Oil and Gas Reserves Information promulgated by the Society of Petroleum Engineers (SPE Standards). We used standard engineering and geoscience methods, or a combination of
methods, including performance analysis, volumetric analysis, and analogy, that we considered to be appropriate and necessary to establish reserves quantities and reserves categorization that conform to SEC definitions and guidelines. In addition,
we believe that the assumptions, data, methods, and procedures used in connection with the preparation of this report are appropriate for the purpose served by the report. Our expertise is in petroleum engineering, geoscience, and petrophysical
interpretation, not legal or accounting matters; we are not accountants, attorneys, or landmen. As in all aspects of oil and gas evaluation, there are uncertainties inherent in the interpretation of engineering and geoscience data; therefore, our
conclusions necessarily represent only informed professional judgment.

This audit was conducted within the context of our
understanding of the effects of petroleum legislation, taxation, and other regulations that currently pertain to the properties. We are not aware of any potential regulation



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amendments that could affect the ability of Repsol to recover the estimated reserves. The data used in our estimates were obtained from Repsol, public data sources, and the nonconfidential files
of Netherland, Sewell & Associates, Inc. (NSAI) and were accepted as accurate. Supporting geoscience, field performance, and work data are on file in our office. The titles to the properties have not been examined by NSAI, nor has the
actual degree or type of interest owned been independently confirmed. The technical persons responsible for preparing the reserves estimates presented herein meet the requirements regarding qualifications, independence, objectivity, and
confidentiality set forth in the SPE Standards; certificates of qualification are included after the definitions as Exhibits I and II. We are independent petroleum engineers, geologists, geophysicists, and petrophysicists; we do not own an interest
in these properties nor are we employed on a contingent basis.



|                               |  |                                     |  |                                |  |                                                                                  |  |                                      |  | 
|------------------------------ |  | ----------------------------------- |  | ------------------------------ |  | -------------------------------------------------------------------------------- |  | ------------------------------------ |  | 
|                               |  |                                     |  |                                |  | Sincerely,                                                                       |  |                                     
|                               |  |                                     | 
|                               |  |                                     |  |                                |  | NETHERLAND, SEWELL & ASSOCIATES, INC. Texas Registered Engineering Firm F-002699
|                               |  |                                     |  |                                | 
|                               |  |                                     |  |                                |  |                                                                                  |  | /s/ C.H. (Scott) Rees III            |  | 
|                               |  |                                     |  |                                |  | By:                                                                              |  |                                      |  | 
|                               |  |                                     |  |                                |  |                                                                                  |  | C.H. (Scott) Rees III, P.E.          |  | 
|                               |  |                                     |  |                                |  |                                                                                  |  | Chairman and Chief Executive Officer |  | 
|                               |  |                                     |  |                                | 
|                               |  | /s/ Philip S. (Scott) Frost         |  |                                |  |                                                                                  |  | /s/ Allen E. Evans, Jr.              |  | 
|By:                            |  |                                     |  |                                |  | By:                                                                              |  |                                      |  | 
|                               |  | Philip S. (Scott) Frost, P.E. 88738 |  |                                |  |                                                                                  |  | Allen E. Evans, Jr., P.G. 1286       |  | 
|                               |  | Senior Vice President               |  |                                |  |                                                                                  |  | Vice President                       |  | 
|                               |  |                                    
|Date Signed:  January 27, 2011 |  |                                     |  | Date Signed:  January 27, 2011

EJS:DSR





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DEFINITIONS OF OIL AND GAS RESERVES

Adapted from U.S. Securities and Exchange Commission Regulation S-X Section 210.4-10(a)



The following definitions are set forth in U.S. Securities and Exchange Commission (SEC)
Regulation S-X Section 210.4-10(a). Also included is supplemental information from (1) the 2007 Petroleum Resources Management System approved by the Society of Petroleum Engineers, (2) the FASB Accounting Standards Codification Topic
932, Extractive ActivitiesOil and Gas, and (3) the SECs Compliance and Disclosure Interpretations.

(1)
Acquisition of properties.  Costs incurred to purchase, lease or otherwise acquire a property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land
including mineral rights is purchased in fee, brokers fees, recording fees, legal costs, and other costs incurred in acquiring properties.

(2) Analogous reservoir.  Analogous reservoirs, as used in resources assessments, have similar rock and fluid properties, reservoir conditions (depth, temperature, and pressure) and drive
mechanisms, but are typically at a more advanced stage of development than the reservoir of interest and thus may provide concepts to assist in the interpretation of more limited data and estimation of recovery. When used to support proved reserves,
an analogous reservoir refers to a reservoir that shares the following characteristics with the reservoir of interest:



| | (i) | Same geological formation (but not necessarily in pressure communication with the reservoir of interest);
| | --- | ---------------------------------------------------------------------------------------------------------

| | (ii) | Same environment of deposition;
| | ---- | -------------------------------

| | (iii) | Similar geological structure; and
| | ----- | ---------------------------------

| | (iv) | Same drive mechanism.
| | ---- | ---------------------

Instruction to paragraph (a)(2): Reservoir properties must, in the aggregate, be no more favorable in the analog than in the reservoir of interest.

(3) Bitumen.  Bitumen, sometimes referred to as natural bitumen, is petroleum in a solid or semi-solid state in natural
deposits with a viscosity greater than 10,000 centipoise measured at original temperature in the deposit and atmospheric pressure, on a gas free basis. In its natural state it usually contains sulfur, metals, and other non-hydrocarbons.

(4) Condensate.  Condensate is a mixture of hydrocarbons that exists in the gaseous phase at original reservoir temperature
and pressure, but that, when produced, is in the liquid phase at surface pressure and temperature.

(5) Deterministic
estimate.  The method of estimating reserves or resources is called deterministic when a single value for each parameter (from the geoscience, engineering, or economic data) in the reserves calculation is used in the reserves
estimation procedure.

(6) Developed oil and gas reserves.  Developed oil and gas reserves are reserves of any
category that can be expected to be recovered:



| | (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.
| | ---- | --------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |  | 
| |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |  | 
| |  | Supplemental definitions from the 2007 Petroleum Resources Management System: 
Developed Producing Reserves  Developed Producing Reserves are expected to be recovered from completion intervals that are open and
producing at the time of the estimate. Improved recovery reserves are considered producing only after the improved recovery project is in operation. 
Developed Non-Producing Reserves  Developed Non-Producing Reserves include shut-in and behind-pipe Reserves. Shut-in Reserves are
expected to be recovered from (1) completion intervals which are open at the time of the estimate but which have not yet started producing, (2) wells which were shut-in for market conditions or pipeline connections, or (3) wells not
capable of production for mechanical reasons. Behind-pipe Reserves are expected to be recovered from zones in existing wells which will require additional completion work or future recompletion prior to start of production. In all cases, production
can be initiated or restored with relatively low expenditure compared to the cost of drilling a new well. |  | 

(7) Development costs.  Costs incurred to obtain access to proved reserves and to provide facilities for extracting, treating, gathering and storing the oil and gas. More specifically,
development costs, including depreciation and applicable operating costs of support equipment and facilities and other costs of development activities, are costs incurred to:



| | (i) | Gain access to and prepare well locations for drilling, including surveying well locations for the purpose of determining specific development drilling
sites, clearing ground, draining, road building, and relocating public roads, gas lines, and power lines, to the extent necessary in developing the proved reserves. | 
| | --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (ii) | Drill and equip development wells, development-type stratigraphic test wells, and service wells, including the costs of platforms and of well equipment
such as casing, tubing, pumping equipment, and the wellhead assembly. | 
| | ---- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 



Definitions 
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DEFINITIONS OF OIL AND GAS RESERVES

Adapted from U.S. Securities and Exchange Commission Regulation S-X Section 210.4-10(a)



| | (iii) | Acquire, construct, and install production facilities such as lease flow lines, separators, treaters, heaters, manifolds, measuring devices, and
production storage tanks, natural gas cycling and processing plants, and central utility and waste disposal systems. | 
| | ----- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (iv) | Provide improved recovery systems. | 
| | ---- | ---------------------------------- | 

(8) Development project.  A development project is the means
by which petroleum resources are brought to the status of economically producible. As examples, the development of a single reservoir or field, an incremental development in a producing field, or the integrated development of a group of several
fields and associated facilities with a common ownership may constitute a development project.

(9) Development
well.  A well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive.

(10) Economically producible.  The term economically producible, as it relates to a resource, means a resource which generates revenue that exceeds, or is reasonably expected to exceed, the
costs of the operation. The value of the products that generate revenue shall be determined at the terminal point of oil and gas producing activities as defined in paragraph (a)(16) of this section.

(11) Estimated ultimate recovery (EUR).  Estimated ultimate recovery is the sum of reserves remaining as of a given date and
cumulative production as of that date.

(12) Exploration costs.  Costs incurred in identifying areas that may
warrant examination and in examining specific areas that are considered to have prospects of containing oil and gas reserves, including costs of drilling exploratory wells and exploratory-type stratigraphic test wells. Exploration costs may be
incurred both before acquiring the related property (sometimes referred to in part as prospecting costs) and after acquiring the property. Principal types of exploration costs, which include depreciation and applicable operating costs of support
equipment and facilities and other costs of exploration activities, are:



| | (i) | Costs of topographical, geographical and geophysical studies, rights of access to properties to conduct those studies, and salaries and other expenses
of geologists, geophysical crews, and others conducting those studies. Collectively, these are sometimes referred to as geological and geophysical or G&G costs. | 
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (ii) | Costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, and the
maintenance of land and lease records. | 
| | ---- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (iii) | Dry hole contributions and bottom hole contributions. | 
| | ----- | ----------------------------------------------------- | 

| | (iv) | Costs of drilling and equipping exploratory wells. | 
| | ---- | -------------------------------------------------- | 

| | (v) | Costs of drilling exploratory-type stratigraphic test wells. | 
| | --- | ------------------------------------------------------------ | 

(13) Exploratory well.  An exploratory well is a well drilled
to find a new field or to find a new reservoir in a field previously found to be productive of oil or gas in another reservoir. Generally, an exploratory well is any well that is not a development well, an extension well, a service well, or a
stratigraphic test well as those items are defined in this section.

(14) Extension well.  An extension well is a
well drilled to extend the limits of a known reservoir.

(15) Field.  An area consisting of a single reservoir or
multiple reservoirs all grouped on or related to the same individual geological structural feature and/or stratigraphic condition. There may be two or more reservoirs in a field which are separated vertically by intervening impervious strata, or
laterally by local geologic barriers, or by both. Reservoirs that are associated by being in overlapping or adjacent fields may be treated as a single or common operational field. The geological terms structural feature and
stratigraphic condition are intended to identify localized geological features as opposed to the broader terms of basins, trends, provinces, plays, areas-of-interest, etc.

(16) Oil and gas producing activities.



| | (i) | Oil and gas producing activities include: | 
| | --- | ----------------------------------------- | 



| | (A) | The search for crude oil, including condensate and natural gas liquids, or natural gas (oil and gas) in their natural states and original
locations; | 
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------ | 

| | (B) | The acquisition of property rights or properties for the purpose of further exploration or for the purpose of removing the oil or gas from such
properties; | 
| | --- | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (C) | The construction, drilling, and production activities necessary to retrieve oil and gas from their natural reservoirs, including the acquisition,
construction, installation, and maintenance of field gathering and storage systems, such as: | 
| | --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (1) | Lifting the oil and gas to the surface; and | 
| | --- | ------------------------------------------- | 

| | (2) | Gathering, treating, and field processing (as in the case of processing gas to extract liquid hydrocarbons); and | 
| | --- | ---------------------------------------------------------------------------------------------------------------- | 



Definitions 
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DEFINITIONS OF OIL AND GAS RESERVES

Adapted from U.S. Securities and Exchange Commission Regulation S-X Section 210.4-10(a)



| | (D) | Extraction of saleable hydrocarbons, in the solid, liquid, or gaseous state, from oil sands, shale, coalbeds, or other nonrenewable natural resources
which are intended to be upgraded into synthetic oil or gas, and activities undertaken with a view to such extraction. | 
| | --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

Instruction 1 to paragraph (a)(16)(i): The oil and
gas production function shall be regarded as ending at a terminal point, which is the outlet valve on the lease or field storage tank. If unusual physical or operational circumstances exist, it may be appropriate to regard the terminal
point for the production function as:



| | a. | The first point at which oil, gas, or gas liquids, natural or synthetic, are delivered to a main pipeline, a common carrier, a refinery, or a marine
terminal; and | 
| | -- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ | 

| | b. | In the case of natural resources that are intended to be upgraded into synthetic oil or gas, if those natural resources are delivered to a purchaser
prior to upgrading, the first point at which the natural resources are delivered to a main pipeline, a common carrier, a refinery, a marine terminal, or a facility which upgrades such natural resources into synthetic oil or gas. | 
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

Instruction 2 to paragraph (a)(16)(i): For purposes
of this paragraph (a)(16), the term saleable hydrocarbons means hydrocarbons that are saleable in the state in which the hydrocarbons are delivered.



| | (ii) | Oil and gas producing activities do not include: | 
| | ---- | ------------------------------------------------ | 



| | (A) | Transporting, refining, or marketing oil and gas;
| | --- | -------------------------------------------------

| | (B) | Processing of produced oil, gas, or natural resources that can be upgraded into synthetic oil or gas by a registrant that does not have the legal right
to produce or a revenue interest in such production; | 
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | 

| | (C) | Activities relating to the production of natural resources other than oil, gas, or natural resources from which synthetic oil and gas can be extracted;
or | 
| | --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (D) | Production of geothermal steam.
| | --- | -------------------------------

(17) Possible reserves.  Possible reserves are those additional reserves that are less certain to be recovered than probable reserves.



| | (i) | When deterministic methods are used, the total quantities ultimately recovered from a project have a low probability of exceeding proved plus probable
plus possible reserves. When probabilistic methods are used, there should be at least a 10% probability that the total quantities ultimately recovered will equal or exceed the proved plus probable plus possible reserves estimates. | 
| | --- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (ii) | Possible reserves may be assigned to areas of a reservoir adjacent to probable reserves where data control and interpretations of available data are
progressively less certain. Frequently, this will be in areas where geoscience and engineering data are unable to define clearly the area and vertical limits of commercial production from the reservoir by a defined project. | 
| | ---- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | 

| | (iii) | Possible reserves also include incremental quantities associated with a greater percentage recovery of the hydrocarbons in place than the recovery
quantities assumed for probable reserves. | 
| | ----- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (iv) | The proved plus probable and proved plus probable plus possible reserves estimates must be based on reasonable alternative technical and commercial
interpretations within the reservoir or subject project that are clearly documented, including comparisons to results in successful similar projects. | 
| | ---- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (v) | Possible reserves may be assigned where geoscience and engineering data identify directly adjacent portions of a reservoir within the same accumulation
that may be separated from proved areas by faults with displacement less than formation thickness or other geological discontinuities and that have not been penetrated by a wellbore, and the registrant believes that such adjacent portions are in
communication with the known (proved) reservoir. Possible reserves may be assigned to areas that are structurally higher or lower than the proved area if these areas are in communication with the proved reservoir. | 
| | --- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (vi) | Pursuant to paragraph (a)(22)(iii) of this section, where direct observation has defined a highest known oil (HKO) elevation and the potential exists
for an associated gas cap, proved oil reserves should be assigned in the structurally higher portions of the reservoir above the HKO only if the higher contact can be established with reasonable certainty through reliable technology. Portions of the
reservoir that do not meet this reasonable certainty criterion may be assigned as probable and possible oil or gas based on reservoir fluid properties and pressure gradient interpretations. | 
| | ---- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

(18) Probable reserves.  Probable reserves are those
additional reserves that are less certain to be recovered than proved reserves but which, together with proved reserves, are as likely as not to be recovered.



| | (i) | When deterministic methods are used, it is as likely as not that actual remaining quantities recovered will exceed the sum of estimated proved plus
probable reserves. When probabilistic methods are used, there should be at least a 50% probability that the actual quantities recovered will equal or exceed the proved plus probable reserves estimates. | 
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 



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DEFINITIONS OF OIL AND GAS RESERVES

Adapted from U.S. Securities and Exchange Commission Regulation S-X Section 210.4-10(a)



| | (ii) | Probable reserves may be assigned to areas of a reservoir adjacent to proved reserves where data control or interpretations of available data are less
certain, even if the interpreted reservoir continuity of structure or productivity does not meet the reasonable certainty criterion. Probable reserves may be assigned to areas that are structurally higher than the proved area if these areas are in
communication with the proved reservoir. | 
| | ---- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (iii) | Probable reserves estimates also include potential incremental quantities associated with a greater percentage recovery of the hydrocarbons in place
than assumed for proved reserves. | 
| | ----- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

| | (iv) | See also guidelines in paragraphs (a)(17)(iv) and (a)(17)(vi) of this section. | 
| | ---- | ------------------------------------------------------------------------------ | 

(19) Probabilistic estimate.  The method of estimation of
reserves or resources is called probabilistic when the full range of values that could reasonably occur for each unknown parameter (from the geoscience and engineering data) is used to generate a full range of possible outcomes and their associated
probabilities of occurrence.

(20) Production costs.



| | (i) | Costs incurred to operate and maintain wells and related equipment and facilities, including depreciation and applicable operating costs of support
equipment and facilities and other costs of operating and maintaining those wells and related equipment and facilities. They become part of the cost of oil and gas produced. Examples of production costs (sometimes called lifting costs) are: | 
| | --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 



| | (A) | Costs of labor to operate the wells and related equipment and facilities.
| | --- | -------------------------------------------------------------------------

| | (B) | Repairs and maintenance. | 
| | --- | ------------------------ | 

| | (C) | Materials, supplies, and fuel consumed and supplies utilized in operating the wells and related equipment and facilities. | 
| | --- | ------------------------------------------------------------------------------------------------------------------------- | 

| | (D) | Property taxes and insurance applicable to proved properties and wells and related equipment and facilities. | 
| | --- | ------------------------------------------------------------------------------------------------------------ | 

| | (E) | Severance taxes. | 
| | --- | ---------------- | 



| | (ii) | Some support equipment or facilities may serve two or more oil and gas producing activities and may also serve transportation, refining, and marketing
activities. To the extent that the support equipment and facilities are used in oil and gas producing activities, their depreciation and applicable operating costs become exploration, development or production costs, as appropriate. Depreciation,
depletion, and amortization of capitalized acquisition, exploration, and development costs are not production costs but also become part of the cost of oil and gas produced along with production (lifting) costs identified above. | 
| | ---- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

(21) Proved area.  The part of a property to which proved
reserves have been specifically attributed.

(22) 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. | 
| | --- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 



| | (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 | 
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | 



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DEFINITIONS OF OIL AND GAS RESERVES

Adapted from U.S. Securities and Exchange Commission Regulation S-X Section 210.4-10(a)



| | 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. | 
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

(23) Proved properties.  Properties with proved reserves.

(24) Reasonable certainty.  If deterministic methods are used, reasonable certainty means a high degree of
confidence that the quantities will be recovered. If probabilistic methods are used, there should be at least a 90% probability that the quantities actually recovered will equal or exceed the estimate. A high degree of confidence exists if the
quantity is much more likely to be achieved than not, and, as changes due to increased availability of geoscience (geological, geophysical, and geochemical), engineering, and economic data are made to estimated ultimate recovery (EUR) with time,
reasonably certain EUR is much more likely to increase or remain constant than to decrease.

(25) Reliable
technology.  Reliable technology is a grouping of one or more technologies (including computational methods) that has been field tested and has been demonstrated to provide reasonably certain results with consistency and repeatability
in the formation being evaluated or in an analogous formation.

(26) Reserves.  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. In addition, there must exist, or there must be a reasonable expectation
that there will exist, the legal right to produce or a revenue interest in the production, installed means of delivering oil and gas or related substances to market, and all permits and financing required to implement the project.

Note to paragraph (a)(26):  Reserves should not be assigned to adjacent reservoirs isolated by major, potentially sealing,
faults until those reservoirs are penetrated and evaluated as economically producible. Reserves should not be assigned to areas that are clearly separated from a known accumulation by a non-productive reservoir (i.e., absence of reservoir,
structurally low reservoir, or negative test results). Such areas may contain prospective resources (i.e., potentially recoverable resources from undiscovered accumulations).



| |  |                                                                                                                                                                                                                        |  |    |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |  |  |  | 
| |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |  | -- |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |  |  |  | 
| |  | Excerpted from the FASB Accounting Standards Codification Topic 932, Extractive ActivitiesOil and Gas:                                                                                                                |  |    |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
| |  | 932-235-50-30  A
standardized measure of discounted future net cash flows relating to an entitys interests in both of the following shall be disclosed as of the end of the year:                                     |  |    |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
| |  |                                                                                                                                                                                                                        |  | a. |  | Proved oil and gas reserves (see paragraphs
932-235-50-3 through 50-11B)                                                                                                                                                                                                                                                                                                                                                                                                            |  |  |  | 
| |  |                                                                                                                                                                                                                        |  | b. |  | Oil and gas subject to purchase under long-term supply, purchase, or similar agreements and contracts in which the
entityparticipates in the operation of the properties on which the oil or gas is located or otherwise serves as the producer of thosereserves (see paragraph 932-235-50-7).                                                                                                                                                                                      |  |  |  | 
| |  | The standardized measure of discounted
future net cash flows relating to those two types of interests in reserves may be combined for reporting purposes.                                                              |  |    |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
| |  | 932-235-50-31  All of the
following information shall be disclosed in the aggregate and for each geographic area for which reserve quantities are disclosed in accordance with paragraphs 932-235-50-3 through 50-11B: |  |    |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
| |  |                                                                                                                                                                                                                        |  | a. |  | Future cash inflows.  These shall be
computed by applying prices used in estimating the entitys proved oil and gas reserves to the year-end quantities of those reserves. Future price changes shall be considered only to the extent provided by contractual arrangements in existence
at year-end.                                                                                                                                                                               |  |  |  | 
| |  |                                                                                                                                                                                                                        |  | b. |  | Future development and production costs.  These costs shall be computed by estimating the expenditures to be incurred in developing and producing
the proved oil and gas reserves at the end of the year, based on year-end costs and assuming continuation of existing economic conditions. If estimated development expenditures are significant, they shall be presented separately from estimated
production costs.                                                             |  |  |  | 
| |  |                                                                                                                                                                                                                        |  | c. |  | Future income tax expenses.  These expenses shall be computed by applying the appropriate year-end statutory tax rates, with consideration of future
tax rates already legislated, to the future pretax net cash flows relating to the entitys proved oil and gas reserves, less the tax basis of the properties involved. The future income tax expenses shall give effect to tax deductions and tax
credits and allowances relating to the entitys proved oil and gas reserves. |  |  |  | 
| |  |                                                                                                                                                                                                                        |  | d. |  | Future net cash flows.  These amounts are the result of subtracting
future development and production costs and futureincome tax expenses from future cash inflows.                                                                                                                                                                                                                                                                                                                 |  |  |  | 



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DEFINITIONS OF OIL AND GAS RESERVES

Adapted from U.S. Securities and Exchange Commission Regulation S-X Section 210.4-10(a)



|                                                                                                                                                                                                                                                                                                                                     |  |  |  | 
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |  |  |  | 
|e.     Discount.  This amount shall be derived from using a discount rate of
10 percent a year to reflect the timing of the future net cash flows relating to proved oil and gas reserves. f.      Standardized measure of discounted future net cash flows.    This amount is the future net cash flows less the computed discount. |  |  |  | 

(27) Reservoir.  A porous and permeable underground formation containing a natural accumulation of producible oil and/or gas that is confined by impermeable rock or water barriers and is
individual and separate from other reservoirs.

(28) Resources.  Resources are quantities of oil and gas
estimated to exist in naturally occurring accumulations. A portion of the resources may be estimated to be recoverable, and another portion may be considered to be unrecoverable. Resources include both discovered and undiscovered accumulations.

(29) Service well.  A well drilled or completed for the purpose of supporting production in an existing field.
Specific purposes of service wells include gas injection, water injection, steam injection, air injection, salt-water disposal, water supply for injection, observation, or injection for in-situ combustion.

(30) Stratigraphic test well.  A stratigraphic test well is a drilling effort, geologically directed, to obtain information
pertaining to a specific geologic condition. Such wells customarily are drilled without the intent of being completed for hydrocarbon production. The classification also includes tests identified as core tests and all types of expendable holes
related to hydrocarbon exploration. Stratigraphic tests are classified as exploratory type if not drilled in a known area or development type if drilled in a known area.

(31) Undeveloped oil and gas 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. | 
| | ---- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 



|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |  | 
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |  | 
|From the SECs Compliance and Disclosure Interpretations (October 26, 2009):
 Although several types of projects  such as
constructing offshore platforms and development in urban areas, remote locations or environmentally sensitive locations  by their nature customarily take a longer time to develop and therefore often do justify longer time periods, this
determination must always take into consideration all of the facts and circumstances. No particular type of project per se justifies a longer time period, and any extension beyond five years should be the exception, and not the rule.
 Factors that a company should consider in determining
whether or not circumstances justify recognizing reserves even though development may extend past five years include, but are not limited to, the following:
   The
companys level of ongoing significant development activities in the area to be developed (for example, drilling only the minimum number of wells necessary to maintain the lease generally would not constitute significant development
activities);   The companys historical record at completing development of
comparable long-term projects;   The amount of time in which the company has
maintained the leases, or booked the reserves, without significant development activities;
  The extent to which the company has followed a previously adopted development plan (for
example, if a company has changed its development plan several times without taking significant steps to implement any of those plans, recognizing proved undeveloped reserves typically would not be appropriate); and
  The extent to which delays in development are caused by external factors related to the
physical operating environment (for example, restrictions on development on Federal lands, but not obtaining government permits), rather than by internal factors (for example, shifting resources to develop properties with higher
priority). |  | 



| | (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 paragraph (a)(2) of this section, or by other evidence using reliable
technology establishing reasonable certainty. | 
| | ----- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 

(32) Unproved properties.  Properties with no proved reserves.



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CERTIFICATE OF QUALIFICATION

I, Philip S. (Scott) Frost, Registered Professional Engineer, 4500 Thanksgiving Tower, 1601 Elm Street, Dallas, Texas 75201, hereby certify:



|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|I am an employee of Netherland, Sewell & Associates, Inc., which prepared a detailed analysis of certain oil and
gas properties of Repsol YPF. The effective date of this evaluation is December 31, 2009.  I do not have, nor do I expect to receive, any direct or indirect interest in the securities of Repsol YPF or its affiliated companies.
 I attended Tulane University, and I graduated in 1984 with
a Masters Degree in Business Administration; I attended Vanderbilt University, and I graduated in 1979 with a Bachelor of Engineering Degree in Mechanical Engineering; I am a Registered Professional Engineer in the State of Texas, United
States of America; and I have in excess of 32 years of experience in petroleum engineering studies and evaluations.



|    |  |                              
|--- |  | -----------------------------
|By: |  | /s/ Philip S. (Scott) Frost  
|    |  | Philip S. (Scott) Frost, P.E.
|    |  | Senior Vice President        
|    |  | Texas Registration No. 88738 

January 27, 2011

Dallas, Texas





Exhibit I



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CERTIFICATE OF QUALIFICATION

I, Allen E. Evans, Jr., Registered Professional Geoscientist, 4500 Thanksgiving Tower, 1601 Elm Street, Dallas, Texas 75201, hereby certify:



|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|I am an employee of Netherland, Sewell & Associates, Inc., which prepared a detailed analysis of certain oil and
gas properties of Repsol YPF. The effective date of this evaluation is December 31, 2009.  I do not have, nor do I expect to receive, any direct or indirect interest in the securities of Repsol YPF or its affiliated companies.
 I attended Old Dominion University, I graduated in 1987
with a Master of Science Degree in Geology, and I graduated in 1981 with a Bachelor of Science Degree in Geology; I am a Licensed Petroleum Geologist in the State of Texas, United States of America; and I have in excess of 28 years of experience in
geological and geophysical studies and evaluations.



|    |  |                            
|--- |  | ---------------------------
|By: |  | /s/ Allen E. Evans, Jr.    
|    |  | Allen E. Evans, Jr., P.G.  
|    |  | Vice President             
|    |  | Texas Registration No. 1286

January 27, 2011

Dallas, Texas





Exhibit II