----

|   | UNITED STATES |
|--------|---------------|

| Delaware                                  |   | 75-2332176          |
|-------------------------------------------|--------|---------------------|
| (State or other jurisdiction              |   | (I.R.S. Employer    |
| of incorporation or organization)         |   | Identification No.) |
|                                      |   |                |
| 6 Desta Drive, Suite 6500, Midland, Texas |   | 79705               |
| (Address of principal executive office)   |   | (Zip Code)          |

| Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.                                                                                                                                                                                                                                    |  ̈ Yes | x No      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------|-----------|
|                                                                                                                                                                                                                                                                                                                                                       |       |      |
| Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.                                                                                                                                                                                                                               |  ̈ Yes | x No      |
|                                                                                                                                                                                                                                                                                                                                                       |       |      |
| Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.   | x Yes      |  ̈ No |
|                                                                                                                                                                                                                                                                                                                                                       |       |      |
| Indicate by check mark whether the registrant has submitted electronically and posted on its corporate website, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). |  ̈ Yes |  ̈ No |

| Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. x |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer.  See definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act. |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Large accelerated filer  ̈                                                                                                                                                                                                                            |   | Accelerated filer  ̈ |   | Non-accelerated filer  x |   | Smaller reporting company ̈ |   |

| Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). |  ̈ Yes | x No |
|---------------------------------------------------------------------------------------------------------|------------|------|

|   |
|--------|

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|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | Page   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|
| Part I                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 1.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Business                                                                                                                                                    | 3      |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 1A.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Risk Factors                                                                                                                                                | 7      |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 1B.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Unresolved Staff Comments                                                                                                                                   | 10     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 2.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Properties                                                                                                                                                  | 10     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 3.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Legal Proceedings                                                                                                                                           | 11     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 4.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | (Removed and Reserved)                                                                                                                                      | 11     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Part II                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 5.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Market for Registrant's Common Equity, Related                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Stockholder Matters and Issuer Purchases of Equity Securities                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 12     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 6.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Selected Financial Data                                                                                                                                     | 13     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 7.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Management's Discussion and Analysis of                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Financial Condition and Results of Operations                                                                                                                                   | 14     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 7A.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Quantitative and Qualitative Disclosures About Market Risk                                                                                                  | 16     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 8.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Financial Statements and Supplementary Data                                                                                                                 | 17     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 9.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Changes in and Disagreements with Accountants                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | on Accounting and Financial Disclosure                                                                                                                                          | 30     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 9A.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Controls and Procedures                                                                                                                                     | 30     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 9B.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Other Information                                                                                                                                           | 31     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Part III                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 10.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Directors, Executive Officers and Corporate Governance                                                                                                      | 32     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 11.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Executive Compensation                                                                                                                                      | 32     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 12.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Security Ownership of Certain Beneficial Owners and Management and                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Related Stockholder Matters                                                                                                                                                     | 33     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 13.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Certain Relationships and Related Transactions, and Director Independence                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 33     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 14.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Principal Accounting Fees and Services                                                                                                                      | 33     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Part IV                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 15.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Exhibits and Financial Statement Schedules                                                                                                                  | 34     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Glossary of Oil and Gas Terms                                                                                                                   | 35                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Signatures                                                                                                                                      | 37                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |

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| ·   | amends the definition of proved reserves to require the use of average commodity prices based upon the prior 12 month period rather than year-end prices; |
|--------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | expands the type of technologies available to establish reserve estimates and categories; |
|--------------------|-------------------------------------------------------------------------------------------|

| ·   | modifies certain definitions used in estimating proved reserves; |
|--------------------|------------------------------------------------------------------|

| ·   | permits disclosure of probable and possible reserves; and |
|--------------------|-----------------------------------------------------------|

| ·   | permits disclosure of reserves based on different price and cost criteria, such as futures prices or management forecasts. |
|--------------------|----------------------------------------------------------------------------------------------------------------------------|

|                               |   | Proved Developed |    |   | Proved       |   |   | Total       |   |
|------------------------------------|--------|------------------|---------|--------|--------------|--------|--------|-------------|--------|
|                               |   | Producing        |    |   | Nonproducing |   |   | Undeveloped |   |   | Proved |   |
| Oil (Bbls)                         |   |             | 86,000  |   |         |   | -      |        |   |   | - |   |   |   | 86,000 |   |
| Gas (Mcf)                          |   |             | 129,000 |   |         |   | -      |        |   |   | 77,000 |   |   |   | 206,000 |   |
| Total (BOE)                        |   |             | 107,000 |   |         |   | -      |        |   |   | 13,000 |   |   |   | 120,000 |   |
|                               |   |             |    |   |         |   |   |        |   |   |   |   |   |   |   |   |
| Standardized measure of discounted |   |             |    |   |         |   |   |        |   |   |   |   |   |   |   |   |
| future net cash flows              |   |             |    |   |         |   |   |        |   |   |   |   |   | $ | 2,125,000 |   |

|   |   | Proved Reserves |   |   |   |   |
|--------|--------|-----------------|--------|--------|--------|--------|
|   |   |            |   |   |   |   |   | Total Oil |   |   | Percent of |   |
|   |   | Oil             |   |   | Gas    |   |   | Equivalent |   |   | Total Oil |   |
|   |   | (Bbls)          |   |   | (Mcf)  |   |   | (BOE) |   |   | Equivalent |   |
| Vacuum |   |            | 49,000 |   |   |   | 18,000 |   |   |   | 52,000 |   |   |   | 43.4 | % |
| Malaga |   |            | 8,000  |   |   |   | 123,000 |   |   |   | 28,000 |   |   |   | 23.3 | % |
| Jalmat |   |            | 12,000 |   |   |   | 41,000 |   |   |   | 19,000 |   |   |   | 15.8 | % |
| Other  |   |            | 17,000 |   |   |   | 24,000 |   |   |   | 21,000 |   |   |   | 17.50 | % |
| Total  |   |            | 86,000 |   |   |   | 206,000 |   |   |   | 120,000 |   |   |   | 100.0 | % |

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| Item 5. | Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities |
|---------|--------------------------------------------------------------------------------------------------------------|

|           |   | Total Number |   |   |          |   |
|----------------|--------|--------------|--------|--------|---------------|--------|
|           |   | of Units     |   |   | Average Price |   |
| Period         |   | Purchased    |   |   | Paid Per Unit |   |
| January 2010   |   |         | -      |   |          | $      | - |   |
| February 2010  |   |         | -      |   |          |   | - |   |
| March 2010     |   |         |   |   |          |   |   |   |
| April 2010     |   |         | -      |   |          |   | - |   |
| May 2010       |   |         | -      |   |          |   | - |   |
| June 2010      |   |         | 55.0   |   |          |   | 36.80 |   |
| July 2010      |   |         | -      |   |          |   | - |   |
| August 2010    |   |         | -      |   |          |   | - |   |
| September 2010 |   |         | 44.0   |   |          |   | 16.53 |   |
| October 2010   |   |         | -      |   |          |   | - |   |
| November 2010  |   |         | -      |   |          |   | - |   |
| December 2010  |   |         | -      |   |          |   | - |   |
| TOTALS         |   |         | 99.0   |   |          | $      | 27.79 |   |

|   |
|--------|

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|                           |   | Years ended December 31, |    |
|--------------------------------|--------|--------------------------|---------|
|                           |   | 2010                     |    |   | 2009 |   |   | 2008 |   |   | 2007 |   |   | 2006 |   |
| Revenues                       |   | $                        | 884,576 |   |   | $ | 737,142 |   |   | $ | 1,346,111 |   |   | $ | 1,054,805 |   |   | $ | 1,040,125 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net income                     |   |                     | 311,677 |   |   |   | 192,711 |   |   |   | 672,543 |   |   |   | 504,105 |   |   |   | 543,105 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Partners' share of net income: |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| General partners               |   |                     | 34,225  |   |   |   | 23,391 |   |   |   | 70,502 |   |   |   | 53,697 |   |   |   | 57,202 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Limited partners               |   |                     | 277,452 |   |   |   | 169,320 |   |   |   | 602,041 |   |   |   | 450,408 |   |   |   | 485,903 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Limited partners’        |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| net income per unit            |   |                     | 25.48   |   |   |   | 15.55 |   |   |   | 55.29 |   |   |   | 41.36 |   |   |   | 44.62 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Limited partners'              |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| cash distributions per unit    |   |                     | 29.67   |   |   |   | 16.88 |   |   |   | 67.22 |   |   |   | 38.95 |   |   |   | 52.63 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Total assets                   |   | $                        | 467,558 |   |   | $ | 498,798 |   |   | $ | 539,804 |   |   | $ | 678,373 |   |   | $ | 619,464 |   |

|   |
|--------|

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| Item 7. | Management's Discussion and Analysis of Financial Condition and Results of Operations |
|---------|---------------------------------------------------------------------------------------|

|   |
|--------|

----

|                                      |   | Year Ended December 31, |    |
|-------------------------------------------|--------|-------------------------|---------|
|                                      |   | 2010                    |    |   | 2009 |   |   | 2008 |   |
| Oil production in barrels                 |   |                    | 9,417   |   |   |   | 10,444 |   |   |   | 10,022 |   |
| Gas production in mcf                     |   |                    | 30,613  |   |   |   | 30,526 |   |   |   | 31,501 |   |
| Total (BOE)                               |   |                    | 14,519  |   |   |   | 15,532 |   |   |   | 15,272 |   |
| Average price per barrel of oil           |   | $                       | 75.72   |   |   | $ | 57.15 |   |   | $ | 103.85 |   |
| Average price per mcf of gas              |   | $                       | 5.60    |   |   | $ | 4.59 |   |   | $ | 9.65 |   |
| Partnership distributions                 |   | $                       | 359,345 |   |   | $ | 204,618 |   |   | $ | 813,179 |   |
| Limited partner distributions             |   | $                       | 323,110 |   |   | $ | 183,819 |   |   | $ | 731,961 |   |
| Per unit distribution to limited partners |   | $                       | 29.67   |   |   | $ | 16.88 |   |   | $ | 67.22 |   |
| Number of limited partner units           |   |                    | 10,889  |   |   |   | 10,889 |   |   |   | 10,889 |   |

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|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   | Page   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|--------|
| Report of Independent Registered Public Accounting Firm                                                                                                    |   | 18     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Balance Sheets                                                                                                                                             |   | 19     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Statements of Operations                                                                                                                                   |   | 20     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Statements of Changes in Partners' Equity                                                                                                                  |   | 21     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Statements of Cash Flows                                                                                                                                   |   | 22     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Notes to Financial Statements                                                                                                                              |   | 23     |

|   |
|--------|

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Report 

|   |
|--------|

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Southwest 

|                                     |   | December 31, |      |
|------------------------------------------|--------|--------------|-----------|
|                                     |   | 2010         |      |   | 2009 |   |
|                                     |   |         |      |   |   |   |
| Assets                                   |   |         |      |   |   |   |
|                                     |   |         |      |   |   |   |
| Current assets:                          |   |         |      |   |   |   |
| Cash and cash equivalents                |   | $            | 83,202    |   |   | $ | 54,536 |   |
| Receivable from Managing General Partner |   |         | 43,716    |   |   |   | 86,237 |   |
| New Mexico income tax deposit            |   |         | 35,121    |   |   |   | 28,179 |   |
| Total current assets                     |   |         | 162,039   |   |   |   | 168,952 |   |
|                                     |   |         |      |   |   |   |   |   |
| Oil and gas properties - using the full- |   |         |      |   |   |   |   |   |
| cost method of accounting                |   |         | 4,274,141 |   |   |   | 4,267,893 |   |
| Less accumulated depreciation,           |   |         |      |   |   |   |   |   |
| depletion and amortization               |   |         | 3,968,622 |   |   |   | 3,938,047 |   |
| Net oil and gas properties               |   |         | 305,519   |   |   |   | 329,846 |   |
|                                     |   |         |      |   |   |   |   |   |
|                                     |   | $            | 467,558   |   |   | $ | 498,798 |   |
|                                     |   |         |      |   |   |   |   |   |
| Liabilities and Partners' Equity         |   |         |      |   |   |   |   |   |
|                                     |   |         |      |   |   |   |   |   |
| Asset retirement obligation              |   | $            | 311,997   |   |   | $ | 295,569 |   |
|                                     |   |         |      |   |   |   |   |   |
| Partners' equity:                        |   |         |      |   |   |   |   |   |
| General partners                         |   |         | 18,122    |   |   |   | 20,132 |   |
| Limited partners                         |   |         | 137,439   |   |   |   | 183,097 |   |
| Total partners' equity                   |   |         | 155,561   |   |   |   | 203,229 |   |
|                                     |   |         |      |   |   |   |   |   |
|                                     |   | $            | 467,558   |   |   | $ | 498,798 |   |

|   |
|--------|

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Southwest 

|                                     |   | Years ended December 31, |    |
|------------------------------------------|--------|--------------------------|---------|
|                                     |   | 2010                     |    |   | 2009 |   |   | 2008 |   |
| Revenues                                 |   |                     |    |   |   |   |   |   |   |
| Oil and gas income                       |   | $                        | 884,432 |   |   | $ | 736,893 |   |   | $ | 1,344,811 |   |
| Interest income                          |   |                     | 144     |   |   |   | 108 |   |   |   | 1,286 |   |
| Other income                             |   |                     | -       |   |   |   | 141 |   |   |   | 14 |   |
|                                     |   |                     | 884,576 |   |   |   | 737,142 |   |   |   | 1,346,111 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Expenses                                 |   |                     |    |   |   |   |   |   |   |   |   |   |
| Production                               |   |                     | 427,202 |   |   |   | 378,151 |   |   |   | 521,531 |   |
| Depreciation, depletion and amortization |   |                     | 30,575  |   |   |   | 41,202 |   |   |   | 32,479 |   |
| Accretion expense                        |   |                     | 17,344  |   |   |   | 27,314 |   |   |   | 20,912 |   |
| General and administrative               |   |                     | 97,778  |   |   |   | 97,764 |   |   |   | 98,646 |   |
|                                     |   |                     | 572,899 |   |   |   | 544,431 |   |   |   | 673,568 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Net income                               |   | $                        | 311,677 |   |   | $ | 192,711 |   |   | $ | 672,543 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Net income allocated to:                 |   |                     |    |   |   |   |   |   |   |   |   |   |
| Managing General Partner                 |   | $                        | 30,803  |   |   | $ | 21,052 |   |   | $ | 63,452 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| General Partner                          |   | $                        | 3,422   |   |   | $ | 2,339 |   |   | $ | 7,050 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Limited partners                         |   | $                        | 277,452 |   |   | $ | 169,320 |   |   | $ | 602,041 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Per limited partner unit                 |   | $                        | 25.48   |   |   | $ | 15.55 |   |   | $ | 55.29 |   |

|   |
|--------|

----

Southwest 

|                         |   | General  |    |   | Limited  |   |     |   |   |
|------------------------------|--------|----------|---------|--------|----------|--------|----------|--------|--------|
|                         |   | Partners |    |   | Partners |   |     | Total  |   |
| Balance at December 31, 2007 |   | $        | 28,256  |   |     | $      | 327,516  |   |   | $ | 355,772 |   |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Net income                   |   |     | 70,502  |   |     |   | 602,041  |   |   |   | 672,543 |   |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Distributions                |   |     | (81,218 | )      |     |   | (731,961 | )      |   |   | (813,179 | ) |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Balance at December 31, 2008 |   |     | 17,540  |   |     |   | 197,596  |   |   |   | 215,136 |   |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Net income                   |   |     | 23,391  |   |     |   | 169,320  |   |   |   | 192,711 |   |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Distributions                |   |     | (20,799 | )      |     |   | (183,819 | )      |   |   | (204,618 | ) |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Balance at December 31, 2009 |   |     | 20,132  |   |     |   | 183,097  |   |   |   | 203,229 |   |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Net income                   |   |     | 34,225  |   |     |   | 277,452  |   |   |   | 311,677 |   |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Distributions                |   |     | (36,235 | )      |     |   | (323,110 | )      |   |   | (359,345 | ) |
|                         |   |     |    |   |     |   |     |   |   |   |   |   |
| Balance at December 31, 2010 |   | $        | 18,122  |   |     | $      | 137,439  |   |   | $ | 155,561 |   |

|   |
|--------|

----

Southwest 

|                                                 |   | Years ended December 31, |     |
|------------------------------------------------------|--------|--------------------------|----------|
|                                                 |   | 2010                     |     |   | 2009 |   |   | 2008 |   |
| Cash flows from operating activities:                |   |                     |     |   |   |   |   |   |   |
| Cash received from oil and gas sales                 |   | $                        | 920,011  |   |   | $ | 683,954 |   |   | $ | 1,470,519 |   |
| Cash paid to suppliers                               |   |                     | (525,756 | ) |   |   | (488,262 | ) |   |   | (632,728 | ) |
| Interest received                                    |   |                     | 144      |   |   |   | 108 |   |   |   | 1,286 |   |
| Other income                                         |   |                     | -        |   |   |   | 141 |   |   |   | 14 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net cash provided by operating activities            |   |                     | 394,399  |   |   |   | 195,941 |   |   |   | 839,091 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Cash flows used in investing activities:             |   |                     |     |   |   |   |   |   |   |   |   |   |
| Additions to oil and gas properties                  |   |                     | (6,388   | ) |   |   | (3,619 | ) |   |   | (6,496 | ) |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Cash flows used in financing activities:             |   |                     |     |   |   |   |   |   |   |   |   |   |
| Distributions to partners                            |   |                     | (359,345 | ) |   |   | (204,618 | ) |   |   | (813,179 | ) |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net increase (decrease) in cash and cash equivalents |   |                     | 28,666   |   |   |   | (12,296 | ) |   |   | 19,416 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Beginning of year                                    |   |                     | 54,536   |   |   |   | 66,832 |   |   |   | 47,416 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| End of year                                          |   | $                        | 83,202   |   |   | $ | 54,536 |   |   | $ | 66,832 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Reconciliation of net income to net                  |   |                     |     |   |   |   |   |   |   |   |   |   |
| cash provided by operating activities:               |   |                     |     |   |   |   |   |   |   |   |   |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net income                                           |   | $                        | 311,677  |   |   | $ | 192,711 |   |   | $ | 672,543 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Adjustments to reconcile net income to               |   |                     |     |   |   |   |   |   |   |   |   |   |
| net cash provided by operating activities:           |   |                     |     |   |   |   |   |   |   |   |   |   |
| Depreciation, depletion and amortization             |   |                     | 30,575   |   |   |   | 41,202 |   |   |   | 32,479 |   |
| Accretion expense                                    |   |                     | 17,344   |   |   |   | 27,314 |   |   |   | 20,912 |   |
| Settlement of asset retirement obligations           |   |                     |     |   |   |   |   |   |   |   |   |   |
| for plugged and abandoned wells                      |   |                     | (776     | ) |   |   | (12,347 | ) |   |   | (12,551 | ) |
| Decrease (increase) in receivables and deposits      |   |                     | 35,579   |   |   |   | (52,939 | ) |   |   | 125,708 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net cash provided by operating activities            |   | $                        | 394,399  |   |   | $ | 195,941 |   |   | $ | 839,091 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Noncash investing and financing activities:          |   |                     |     |   |   |   |   |   |   |   |   |   |
| Decrease in oil and gas properties  -      |   |                     |     |   |   |   |   |   |   |   |   |   |
| Asset retirement obligations                         |   | $                        | (140     | ) |   | $ | (44,066 | ) |   | $ | (6,294 | ) |

|   |
|--------|

----

Southwest 

| 1. | Organization |
|----|--------------|

|                                                                | Limited  |   | General  |
|---------------------------------------------------------------------|----------|--------|----------|
|                                                                | Partners |   | Partners |
| Interest income on capital contributions                            | 100%     |   | -        |
| Oil and gas sales                                                   | 90%      |   | 10%      |
| All other revenues                                                  | 90%      |   | 10%      |
| Organization and offering costs (1)                                 | 100%     |   | -        |
| Amortization or organization costs                                  | 100%     |   | -        |
| Property acquisition costs                                          | 100%     |   | -        |
| Gain/loss on property disposition                                   | 90%      |   | 10%      |
| Operating and administrative costs (2)                              | 90%      |   | 10%      |
| Depreciation, depletion, and amortization of oil and gas properties | 100%     |   | -        |
| All other costs                                                     | 90%      |   | 10%      |

|   | (1) | All organization costs in excess of 3% of initial capital contributions will be paid by the Managing General Partner and will be treated as a capital contribution.  The Partnership paid the Managing General Partner an amount equal to 3% of initial capital contributions for such organization costs. |
|--------|-----|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   | (2) | Administrative costs in any year, which exceed 2% of capital contributions shall be paid by the Managing General Partner and will be treated as a capital contribution. |
|--------|-----|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| 2. | Summary of Significant Accounting Policies |
|----|--------------------------------------------|

|   |
|--------|

----

| 2. | Summary of Significant Accounting Policies- continued |
|----|-------------------------------------------------------|

|   |
|--------|

----

|                                                        |   | 2010   |    |   | 2009   |   |
|-------------------------------------------------------------|--------|--------|---------|--------|--------|--------|
| Beginning of year                                           |   | $      | 295,569 |   |   | $      | 324,668 |   |
| Reduction of obligations due to wells plugged and abandoned |   |   | (776    | )      |   |   | (12,347 | ) |
| Accretion expense                                           |   |   | 17,344  |   |   |   | 27,314 |   |
| Revisions of previous estimates                             |   |   | (140    | )      |   |   | (44,066 | ) |
| End of year                                                 |   | $      | 311,997 |   |   | $      | 295,569 |   |

| 4. | Commitments and Contingent Liabilities |
|----|----------------------------------------|

|   |
|--------|

----

| 5. | Related Party Transactions |
|----|----------------------------|

| 6. | Oil and Gas Reserves Information (unaudited) |
|----|----------------------------------------------|

| ·   | amends the definition of proved reserves to require the use of average commodity prices based upon the prior 12-month period rather than year-end prices; |
|--------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | expands the type of technologies available to establish reserve estimates and categories; |
|--------------------|-------------------------------------------------------------------------------------------|

| ·   | modifies certain definitions used in estimating proved reserves; |
|--------------------|------------------------------------------------------------------|

| ·   | permits disclosure of probable and possible reserves; and |
|--------------------|-----------------------------------------------------------|

| ·   | permits disclosure of reserves based on different price and cost criteria, such as futures prices or management forecasts. |
|--------------------|----------------------------------------------------------------------------------------------------------------------------|

|   |
|--------|

----

| 6. | Oil and Gas Reserves Information (unaudited) - continued |
|----|----------------------------------------------------------|

|                            |   | Oil (bbls) |    |   | Gas (mcf) |   |
|---------------------------------|--------|------------|---------|--------|-----------|--------|
| Total Proved -                  |   |       |    |   |      |   |
|                            |   |       |    |   |      |   |
| January 1, 2008                 |   |       | 151,000 |   |      |   | 335,000 |   |
|                            |   |       |    |   |      |   |   |   |
| Revisions of previous estimates |   |       | (55,000 | )      |      |   | (55,000 | ) |
| Production                      |   |       | (10,000 | )      |      |   | (32,000 | ) |
|                            |   |       |    |   |      |   |   |   |
| December 31, 2008               |   |       | 86,000  |   |      |   | 248,000 |   |
|                            |   |       |    |   |      |   |   |   |
| Revisions of previous estimates |   |       | 13,000  |   |      |   | (53,000 | ) |
| Production                      |   |       | (10,000 | )      |      |   | (31,000 | ) |
|                            |   |       |    |   |      |   |   |   |
| December 31, 2009               |   |       | 89,000  |   |      |   | 164,000 |   |
|                            |   |       |    |   |      |   |   |   |
| New discoveries and extensions  |   |       | -       |   |      |   | 77,000 |   |
| Revisions of previous estimates |   |       | 6,000   |   |      |   | (4,000 | ) |
| Production                      |   |       | (9,000  | )      |      |   | (31,000 | ) |
|                            |   |       |    |   |      |   |   |   |
| December 31, 2010               |   |       | 86,000  |   |      |   | 206,000 |   |
|                            |   |       |    |   |      |   |   |   |
| Proved developed reserves -     |   |       |    |   |      |   |   |   |
| December 31, 2008               |   |       | 67,000  |   |      |   | 150,000 |   |
| December 31, 2009               |   |       | 70,000  |   |      |   | 145,000 |   |
| December 31, 2010               |   |       | 86,000  |   |      |   | 129,000 |   |

|   |
|--------|

----

| 6. | Oil and Gas Reserves Information (unaudited) - continued |
|----|----------------------------------------------------------|

|                                          |   | 2010   |      |   | 2009   |   |      | 2008   |   |
|-----------------------------------------------|--------|--------|-----------|--------|--------|--------|-----------|--------|--------|
| Future cash inflows                           |   | $      | 7,285,000 |   |   | $      | 5,316,000 |   |   | $ | 5,167,000 |   |
| Production, development and abandonment costs |   |   | 3,968,000 |   |   |   | 3,547,000 |   |   |   | 3,190,000 |   |
| Future net cash flows                         |   |   | 3,317,000 |   |   |   | 1,769,000 |   |   |   | 1,977,000 |   |
| 10% annual discount for estimated             |   |   |      |   |   |   |      |   |   |   |   |   |
| timing of cash flows                          |   |   | 1,192,000 |   |   |   | 642,000   |   |   |   | 776,000 |   |
| Standardized measure of discounted            |   |   |      |   |   |   |      |   |   |   |   |   |
| future net cash flows                         |   | $      | 2,125,000 |   |   | $      | 1,127,000 |   |   | $ | 1,201,000 |   |

|                                                   |   | 2010   |      |   | 2009   |   |      | 2008   |   |
|--------------------------------------------------------|--------|--------|-----------|--------|--------|--------|-----------|--------|--------|
| Sales of oil and gas produced, net of production costs |   | $      | (457,000  | )      |   | $      | (359,000  | )      |   | $ | (824,000 | ) |
| New discoveries and extensions                         |   |   | 244,000   |   |   |   | -         |   |   |   | - |   |
| Changes in prices and production costs                 |   |   | 963,000   |   |   |   | 53,000    |   |   |   | (3,614,000 | ) |
| Changes of production rates (timing) and others        |   |   | 41,000    |   |   |   | 71,000    |   |   |   | 279,000 |   |
| Revisions of previous quantities estimates             |   |   | 94,000    |   |   |   | 41,000    |   |   |   | (605,000 | ) |
| Accretion of discount                                  |   |   | 113,000   |   |   |   | 120,000   |   |   |   | 542,000 |   |
| Discounted future net cash flows -                     |   |   |      |   |   |   |      |   |   |   |   |   |
| Beginning of year                                      |   |   | 1,127,000 |   |   |   | 1,201,000 |   |   |   | 5,423,000 |   |
| End of year                                            |   | $      | 2,125,000 |   |   | $      | 1,127,000 |   |   | $ | 1,201,000 |   |

|   |
|--------|

----

|                  |   | Quarter |    |
|-----------------------|--------|---------|---------|
|                  |   | First   |    |   | Second |   |   | Third |   |   | Fourth |   |
| 2010:                 |   |    |    |   |   |   |   |   |   |   |   |   |
| Total revenues        |   | $       | 239,446 |   |   | $ | 248,339 |   |   | $ | 200,742 |   |   | $ | 196,049 |   |
| Total expenses        |   |    | 149,521 |   |   |   | 146,331 |   |   |   | 124,111 |   |   |   | 152,936 |   |
| Net income            |   | $       | 89,925  |   |   | $ | 102,008 |   |   | $ | 76,631 |   |   | $ | 43,113 |   |
|                  |   |    |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net income per        |   |    |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| limited partners unit |   | $       | 7.36    |   |   | $ | 8.35 |   |   | $ | 6.27 |   |   | $ | 3.50 |   |

|                  |   | Quarter |    |
|-----------------------|--------|---------|---------|
|                  |   | First   |    |   | Second |   |   | Third |   |   | Fourth |   |
| 2009:                 |   |    |    |   |   |   |   |   |   |   |   |   |
| Total revenues        |   | $       | 116,307 |   |   | $ | 180,303 |   |   | $ | 215,769 |   |   | $ | 224,763 |   |
| Total expenses        |   |    | 157,092 |   |   |   | 123,317 |   |   |   | 134,758 |   |   |   | 129,264 |   |
| Net income (loss)     |   | $       | (40,785 | ) |   | $ | 56,986 |   |   | $ | 81,011 |   |   | $ | 95,499 |   |
|                  |   |    |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net income (loss) per |   |    |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| limited partners unit |   | $       | (3.48   | ) |   | $ | 4.62 |   |   | $ | 6.61 |   |   | $ | 7.80 |   |

|   |
|--------|

----

Item 

Item 

| ·   | management of the Managing General Partner has evaluated the effectiveness of the disclosure controls and procedures as of the end of the period covered by this report; |
|--------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | this evaluation was conducted under the supervision and with the participation of management of the Managing General Partner, including the chief executive and chief financial officers of the Managing General Partner; and |
|--------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | it is the conclusion of chief executive and chief financial officers of the Managing General Partner that these disclosure controls and procedures are effective in ensuring that information that is required to be disclosed by the Partnership in reports filed or submitted with the SEC is recorded, processed, summarized and reported within the time periods specified in the rules and forms established by the SEC. |
|--------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of our assets; |
|--------------------|--------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that our receipts and expenditures are being made only in accordance with authorizations of management and our Board of Directors; and |
|--------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| ·   | provide reasonable assurance regarding prevention or timely detection of any unauthorized acquisition, use or disposition of our assets that could have a material effect on the financial statements. |
|--------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   |
|--------|

----

Item 

|   |
|--------|

----

Item 

Item 

|   |
|--------|

----

Item 

Item 

Item 

| For the Year Ended December 31, |   | 2010   |   |   | 2009   |   |
|---------------------------------|--------|--------|--------|--------|--------|--------|
| Audit Fees                      |   | $      | 19,034 |   |   | $      | 17,163 |   |
| Audit Related Fees              |   |   | -      |   |   |   | - |   |
| Tax Fees                        |   |   | -      |   |   |   | - |   |
| All Other Fees                  |   |   | -      |   |   |   | - |   |
|                            |   |   |   |   |   |   |   |   |
| TOTAL                           |   | $      | 19,034 |   |   | $      | 17,163 |   |

|   |
|--------|

----

Item 

| (a)    | (1)    | Financial Statements:                                                                                                                                                                                |
|--------|--------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |   |                                                                                                                                                                                                 |
|   |   | Included in Part II of this report                                                                                                                                                                   |
|   |   |                                                                                                                                                                                                 |
|   |   | Report of Independent Registered Public Accounting Firm                                                                                                                                              |
|   |   | Balance Sheets                                                                                                                                                                                       |
|   |   | Statements of Operations                                                                                                                                                                             |
|   |   | Statements of Changes in Partners' Equity                                                                                                                                                            |
|   |   | Statements of Cash Flows                                                                                                                                                                             |
|   |   | Notes to Financial Statements                                                                                                                                                                        |
|   |   |                                                                                                                                                                                                 |
|   | (2)    | Schedules required by Article 12 of Regulation S-X are either omitted because they are not applicable or because the required information is shown in the financial statements or the notes thereto. |
|   |   |                                                                                                                                                                                                 |
|   | (3)    | Exhibits:                                                                                                                                                                                            |

| 4      | (a)    | Certificate of Limited Partnership of Southwest Oil & Gas Income Fund X-B, L.P., dated November 27, 1990.  (Incorporated by reference from Partnership's Form 10-K for the fiscal year ended December 31, 1990.) |
|--------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |   |                                                                                                                                                                                                                           |
|   | (b)    | Agreement of Limited Partnership of Southwest Oil & Gas Income Fund X-B, L.P. dated November 27, 1990.  (Incorporated by reference from Partnership's Form 10-K for the fiscal year ended December 31, 1991.)    |
|   |   |                                                                                                                                                                                                                           |
|   | 31.1   | Rule 13a-14(a)/15d-14(a) Certification                                                                                                                                                                                         |
|   | 31.2   | Rule 13a-14(a)/15d-14(a) Certification                                                                                                                                                                                         |
|   | 32.1   | Certification of Chief Executive Officer and Chief Financial Officer Pursuant to 18 U.S.C. Section 1350, as adopted Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002                                                  |

|   |
|--------|

----

Glossary 

|   |
|--------|

----

|   |
|--------|

----

Signatures

|   | Southwest Oil & Gas Income Fund X-B, L.P., |
|--------|------------------------------------------------|
|   | a Delaware limited partnership            |
|   |                                           |
| By:    | Southwest Royalties, Inc., Managing            |
|   | General Partner                                |
|   |                                           |
|   |                                           |
| By:    | /s/ Mel G. Riggs                               |
|   | Mel G. Riggs                                   |
|   | President and Chief Executive Officer          |
|   |                                           |
| Date:  | March 29, 2011                                 |

|                                                                                  |   |                                                                                  |
|---------------------------------------------------------------------------------------|--------|---------------------------------------------------------------------------------------|
| /s/ Clayton W Williams                                                                |   | /s/ Mel G. Riggs                                                                      |
| Clayton W. Williams, Chairman of the Board                                            |   | Mel G. Riggs, President, Chief Executive                                              |
| and a Director                                                                        |   | Officer and a Director                                                                |
|                                                                                  |   |                                                                                  |
| Date:           March 29, 2011 |   | Date:           March 29, 2011 |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |
| /s/ Michael L. Pollard                                                                |   |                                                                                  |
| Michael L. Pollard, Senior Vice President                                             |   |                                                                                  |
| and Chief Financial Officer                                                           |   |                                                                                  |
|                                                                                  |   |                                                                                  |
| Date:           March 29, 2011 |   |                                                                                  |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |