Exhibit 10.4

(1 of 2)



|     |                                                                                                                                              |                           
|---- | -------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------
|LOGO |                                                                                                                                              | PRESIDENT - ROBERT C. BARG
|     | VICE
PRESIDENTS ALLEN E. EVANS, JR.
RANDOLPH K. GREEN JOHN G HATTNER C. H. (SCOTT)
REES III DANNY S. SIMMONS
DAN PAUL SMITH THOMAS M. SOUERS

February 23, 2012

Ing. Carlos A. Morales Gil

Director General

Pemex-Exploración y Producción

Avenida Marina Nacional 329

Torre Ejecutiva,
Piso 41

Col. Petróleos Mexicanos, C.P. 11311

Del. Miguel Hidalgo, México, D.F.

México

Dear Ing. Morales:

In accordance with your
request, we have audited the estimates prepared February 10, 2012, by Pemex-Exploración y Producción (PEP), as of January 1, 2012, of the the gross (100 percent) proved reserves in 28 Northeastern Marine Region fields in the
Bay of Campeche, offshore west of the Yucatán Peninsula of Mexico. It is our understanding that the proved reserves estimates shown herein constitute approximately 44.5 percent of all proved reserves owned by the United Mexican States.
Economic analysis was performed by PEP only to confirm economic producibility and determine economic limits for the properties, using the price and cost parameters discussed in subsequent paragraphs of this letter. We have examined the estimates
with respect to reserves quantities, reserves categorization, and future producing rates, using the definitions set forth In U.S. Securities and Exchange Commission (SEC) Regulation S-X Rule 4-10(a). The estimates of reserves have been prepared in
accordance with the definitions and regulations of the SEC and conform to the FASB Accounting Standards Codification Topic 932, Extractive ActivitiesOil and Gas. We completed our audit on or about the date of this letter. This report has been
prepared for Petroleos Mexicanos use in filing with the SEC; in our opinion the assumptions, data, methods, and procedures used in the preparation of this report are appropriate for such purpose.

The following table sets forth PEPs estimates of the gross (100 percent) reserves, as of January 1, 2012, for the audited properties:



|                               |  |                              |         |  |                   |  |      |                      |  |  |                   |  |  |            |       |  |  |  |         | 
|------------------------------ |  | ---------------------------- | ------- |  | ----------------- |  | ---- | -------------------- |  |  | ----------------- |  |  | ---------- | ----- |  |  |  | ------- | 
|                               |  | Gross (100 Percent) Reserves |        
|Category                       |  | Crude Oil(MMBBL)             |         |  | Condensate(MMBBL) |  |      | Plant Liquids(MMBBL) |  |  | Dry Gas(1)(MMBOE) |  |  | BOE(MMBBL) |      
|                               |  |                              |         |  |                  
|Proved Developed Producing     |  |                              | 3,217.2 |  |                   |  | 60.3 |                      |  |  | 108.5             |  |  |            | 213.7 |  |  |  | 3,599.7 | 
|Proved Developed Non-Producing |  |                              | 1,085.8 |  |                   |  | 19.2 |                      |  |  | 41.2              |  |  |            | 81.0  |  |  |  | 1,227.2 | 
|Proved Undeveloped             |  |                              | 1,225.1 |  |                   |  | 13.7 |                      |  |  | 23.9              |  |  |            | 49.8  |  |  |  | 1,312.5 | 
|                               |  |                              |         |  |                   |  |      |                      |  |  |                   |  |  |            |       |  |  |  |         | 
|                               |  |                              |         |  |                  
|Total Proved                   |  |                              | 5,528.0 |  |                   |  | 93.2 |                      |  |  | 173.6             |  |  |            | 344.6 |  |  |  | 6,139.4 | 

Totals may not add because of rounding.



|(1) | Dry gas reserves are the dry, sweetened gas available for sale by Pemex-Gas y Petroquimica Básica at the tailgate of the processing plants.
|--- | -------------------------------------------------------------------------------------------------------------------------------------------

Crude oil, condensate, plant liquids, and barrels of oil equivalent (BOE) volumes are expressed in millions of barrels
(MMBBL); a barrel is equivalent to 42 United States gallons. Dry gas volumes are expressed in millions of barrels of oil equivalent (MMBOE), determined using dry gas conversion factors provided by PEP.

1601 ELM STREET, SUITE 4500  DALLAS, TEXAS 75201-4754
 PH: 214-969-5401  FAX: 214-969-5411



---

LOGO



When compared on a field-by-field basis, some of the estimates of PEP are greater and some are less than
the estimates of Netherland, Sewell International, S. de R.L. de C.V. (NSI). However, in our opinion the estimates of gross proved reserves prepared by PEP shown herein are, in the aggregate, reasonable and 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). Additionally, these estimates are within the recommended 10 percent tolerance threshold set
forth in the SPE Standards. We are satisfied with the methods and procedures used by PEP in preparing the January 1, 2012, estimates of reserves, and we saw nothing of an unusual nature that would cause us to take exception with the estimates,
in the aggregate, as prepared by PEP.

The estimates shown herein are for proved reserves. PEPs estimates do not include probable or
possible reserves that may exist for these properties. 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.

Oil and gas prices were used only to confirm economic producibility and determine economic limits for the properties.
It is our understanding that prices used by PEP are based on the 12-month unweighted arithmetic average of the first-day-of-the-month price for each month in the period January through December 2011. All prices are held constant throughout the lives
of the properties.

Costs were used only to confirm economic producibility and determine economic limits for the properties. Operating costs
used by PEP are based on historical operating expense records. These costs include district and regional overhead expenses along with costs incurred at the field level. No headquarters general and administrative overhead expenses of PEP or
Petróleos Mexicanos are included. PEPs estimates of capital costs are included as required for workovers, new development wells, pipelines, platforms, and production equipment. Based on our understanding of PEPs future development
plans, a review of the records provided to us, and our knowledge of similar properties, we regard these estimated capital costs to be reasonable. Operating costs are held constant throughout the lives of the properties, and capital costs are held
constant to the date of expenditure. Estimates do not include any salvage value for the lease and well equipment or the cost of abandoning the properties.

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; probable and possible reserves are those additional reserves which are sequentially less certain to be recovered than proved reserves. 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, estimates of PEP and NSI 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 PEP to recover the reserves, and that 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 confirm economic producibility and determine economic limits for the properties. 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 these estimates.

It should be understood that our audit
does not constitute a complete reserves study of the audited oil and gas properties. Our audit consisted primarily of substantive testing, wherein we conducted a detailed review of all properties making up the total proved reserves in the
Northeastern Marine Region. In the conduct of our audit, we have not independently verified the accuracy and completeness of information and data furnished by PEP with respect to oil and gas production, well test data, historical costs of operation
and development, product prices, or any agreements relating to current and future operations of the properties and sales of production. However, if in the course of our examination something came to our attention that brought into question the
validity or



---

LOGO



sufficiency of any such information or data, we did not rely on such information or data until we had satisfactorily resolved our questions relating thereto or had independently verified such
information or data. Our audit did not include a review of PEPs overall reserves management processes and practices.

We used standard
engineering and geoscience methods, or a combination of methods, including performance analysis, volumetric analysis, analogy, and reservoir modeling, that we considered to be appropriate and necessary to establish the conclusions set forth herein.
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.

Supporting data documenting this audit, along with data provided by PEP, are on file in our office. The technical persons responsible for conducting this
audit meet the requirements regarding qualifications, independence, objectivity, and confidentiality set forth in the SPE Standards. 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 INTERNATIONAL, S. DE R.L. DE C.V.By:

/s/ Robert C. BargRobert C. Barg, P.E.President




|    |  |                                                                    |  |      |  |     |  |                                                              |  |     
|--- |  | ------------------------------------------------------------------ |  | ---- |  | --- |  | ------------------------------------------------------------ |  | ----
|By: |  | /s/ Randolph K. Green Randolph K. Green, P.E. 72951 Vice President |  | LOGO |  | By: |  | /s/ John G. Hattner John G. Hattner, P.G. 559 Vice President |  | LOGO

|             |  |                   |  |  |  |              |  |                   |  | 
|------------ |  | ----------------- |  |  |  | ------------ |  | ----------------- |  | 
|             |  |                   |  |  | 
|Date Signed: |  | February 23, 2012 |  |  |  | Date Signed: |  | February 23, 2012 |  | 

RKG:VLG



---

Exhibit 10.4

(2 of 2)



|     |                                                                                                                                               |                           
|---- | --------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------
|LOGO |                                                                                                                                               | PRESIDENT - ROBERT C. BARG
|     | VICE
PRESIDENTS ALLEN E. EVANS, JR.
RANDOLPH K. GREEN JOHN G. HATTNER C. H. (SCOTT)
REES III DANNY S. SIMMONS
DAN PAUL SMITH THOMAS M. SOUERS

February 23, 2012

Ing. Carlos A. Morales Gil

Director General

Pemex-Exploración y Producción

Avenida Marina Nacional 329

Torre Ejecutiva,
Piso 41

Col. Petróleos Mexicanos, C.P. 11311

Del. Miguel Hidalgo, México, D.F.

México

Dear Ing. Morales:

In accordance with your
request, we have audited the estimates prepared February 10, 2012, by Pemex- Exploración y Producción (PEP), as of January 1, 2012, of the gross (100 percent) proved reserves in 120 fields of the Southern Region located in
the states of Chiapas, Tabasco, and Veracruz, Mexico. It is our understanding that the proved reserves estimates shown herein constitute approximately 29 percent of all proved reserves owned by the United Mexican States. Economic analysis was
performed by PEP only to confirm economic producibility and determine economic limits for the properties, using the price and cost parameters discussed in subsequent paragraphs of this letter. We have examined the estimates with respect to reserves
quantities, reserves categorization, and future producing rates, using the definitions set forth in U.S. Securities and Exchange Commission (SEC) Regulation S-X Rule 4-10(a). The estimates of reserves have been prepared in accordance with the
definitions and regulations of the SEC and conform to the FASB Accounting Standards Codification Topic 932, Extractive ActivitiesOil and Gas. We completed our audit on or about the date of this letter. This report has been prepared for
Petróleos Mexicanos use in filing with the SEC; in our opinion the assumptions, data, methods, and procedures used in the preparation of this report are appropriate for such purpose.

The following table sets forth PEPs estimates of the gross (100 percent) reserves, as of January 1, 2012, for the audited properties:



|                               |  |                              |         |  |                   |  |       |                      |  |  |                   |  |  |            |       |  |  |  |         | 
|------------------------------ |  | ---------------------------- | ------- |  | ----------------- |  | ----- | -------------------- |  |  | ----------------- |  |  | ---------- | ----- |  |  |  | ------- | 
|                               |  | Gross (100 Percent) Reserves |        
|Category                       |  | Crude Oil(MMBBL)             |         |  | Condensate(MMBBL) |  |       | Plant Liquids(MMBBL) |  |  | Dry Gas(1)(MMBOE) |  |  | BOE(MMBBL) |      
|                               |  |                              |         |  |                  
|Proved Developed Producing     |  |                              | 845.3   |  |                   |  | 27.4  |                      |  |  | 269.4             |  |  |            | 434.9 |  |  |  | 1,577.1 | 
|Proved Developed Non-Producing |  |                              | 712.8   |  |                   |  | 25.7  |                      |  |  | 111.4             |  |  |            | 184.8 |  |  |  | 1,034.7 | 
|Proved Undeveloped             |  |                              | 859.1   |  |                   |  | 61.2  |                      |  |  | 173.0             |  |  |            | 275.1 |  |  |  | 1,368.4 | 
|                               |  |                              |         |  |                   |  |       |                      |  |  |                   |  |  |            |       |  |  |  |         | 
|                               |  |                              |         |  |                  
|Total Proved                   |  |                              | 2,417.2 |  |                   |  | 114.4 |                      |  |  | 553.8             |  |  |            | 894.9 |  |  |  | 3,980.2 | 

Totals may not add because of rounding.



|(1) | Dry gas reserves are the dry, sweetened gas available for sale by Pemex-Gas y Petroquimica Básica at the tailgate of the processing plants.
|--- | -------------------------------------------------------------------------------------------------------------------------------------------

Crude oil, condensate, plant liquids, and barrels of oil equivalent (BOE) volumes are expressed in millions of barrels
(MMBBL); a barrel is equivalent to 42 United States gallons. Dry gas volumes are expressed in millions of barrels of oil equivalent (MMBOE), determined using dry gas conversion factors provided by PEP.

1601 ELM STREET, SUITE 4500  DALLAS, TEXAS 75201-4754
 PH: 214-969-5401  FAX: 214-969-5411



---

LOGO



When compared on a field-by-field basis, some of the estimates of PEP are greater and some are less than
the estimates of Netherland, Sewell International, S. de R.L. de C.V. (NSI). However, in our opinion the estimates of gross proved reserves prepared by PEP shown herein are, in the aggregate, reasonable and 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). Additionally, these estimates are within the recommended 10 percent tolerance threshold set
forth in the SPE Standards. We are satisfied with the methods and procedures used by PEP in preparing the January 1, 2012, estimates of reserves, and we saw nothing of an unusual nature that would cause us to take exception with the estimates,
in the aggregate, as prepared by PEP.

The estimates shown herein are for proved reserves. PEPs estimates do not include probable or
possible reserves that may exist for these properties. 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.

Oil and gas prices were used only to confirm economic producibility and determine economic limits for the properties.
It is our understanding that prices used by PEP are based on the 12-month unweighted arithmetic average of the first-day-of-the-month price for each month in the period January through December 2011. All prices are held constant throughout the lives
of the properties.

Costs were used only to confirm economic producibility and determine economic limits for the properties. Operating costs
used by PEP are based on historical operating expense records. These costs include district and regional overhead expenses along with costs incurred at the field level. No headquarters general and administrative overhead expenses of PEP or
Petróleos Mexicanos are included. PEPs estimates of capital costs are included as required for workovers, new development wells, and production equipment. Based on our understanding of PEPs future development plans, a review of
the records provided to us, and our knowledge of similar properties, we regard these estimated capital costs to be reasonable. Operating costs are held constant throughout the lives of the properties, and capital costs are held constant to the date
of expenditure. Estimates do not include any salvage value for the lease and well equipment or the cost of abandoning the properties.

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; probable and possible reserves are those additional reserves which are sequentially less certain to be recovered than proved reserves. 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, estimates of PEP and NSI 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 PEP to recover the
reserves, and that 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 confirm
economic producibility and determine economic limits for the properties. 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 these estimates.

It should be understood that our audit does not constitute a complete reserves
study of the audited oil and gas properties. Our audit consisted primarily of substantive testing, wherein we conducted a detailed review of major properties making up approximately 90 percent of the companys total proved reserves in the
Southern Region. In the conduct of our audit, we have not independently verified the accuracy and completeness of information and data furnished by PEP with respect to oil and gas production, well test data, historical costs of operation and
development, product prices, or any agreements relating to current and future operations of the properties and sales of production. However, if in the course of our examination something came to our attention that brought into question the validity
or sufficiency of any such information or data, we did not rely on such information or data until we had satisfactorily resolved our questions relating thereto or had independently verified such information or data. Our audit did not include a
review of PEPs overall reserves management processes and practices.



---

LOGO



We used standard engineering and geoscience methods, or a combination of methods, including performance
analysis, volumetric analysis, analogy, and reservoir modeling, that we considered to be appropriate and necessary to establish the conclusions set forth herein. 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.

Supporting data documenting this audit, along with data provided by PEP, are on file in our office. The technical persons responsible for conducting this
audit meet the requirements regarding qualifications, independence, objectivity, and confidentiality set forth in the SPE Standards. 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 INTERNATIONAL, S. DE R.L. DE C.V.By:

/s/ Robert C. BargRobert C. Barg, P.E.President




|    |  |                                                              |  |      |  |     |  |                                                                      |  |     
|--- |  | ------------------------------------------------------------ |  | ---- |  | --- |  | -------------------------------------------------------------------- |  | ----
|By: |  | /s/ Dan Paul Smith Dan Paul Smith, P.E. 49093 Vice President |  | LOGO |  | By: |  | /s/ Allen E. Evans Jr. Allen E. Evans, Jr., P.G. 1286 Vice President |  | LOGO

|             |  |                   |  |  |  |              |  |                   |  | 
|------------ |  | ----------------- |  |  |  | ------------ |  | ----------------- |  | 
|             |  |                   |  |  | 
|Date Signed: |  | February 23, 2012 |  |  |  | Date Signed: |  | February 23, 2012 |  | 

DPS:ART