----

| Delaware                                  |   | 75-2332174          |
|-------------------------------------------|--------|---------------------|
| (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                                                                                                                                   | 8      |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 2.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Properties                                                                                                                                                  | 9      |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 3.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Legal Proceedings                                                                                                                                           | 10     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 4.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Submission of Matters to a Vote of Security Holders                                                                                                         | 10     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Part II                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 5.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Market for Registrant's Common Equity, Related                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Stockholder Matters and Issuer Purchases of Equity Securities                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 11     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 6.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Selected Financial Data                                                                                                                                     | 12     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 7.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Management's Discussion and Analysis of                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Financial Condition and Results of Operations                                                                                                                                   | 13     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 7A.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Quantitative and Qualitative Disclosures About Market Risk                                                                                                  | 15     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 8.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Financial Statements and Supplementary Data                                                                                                                 | 16     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 9.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Changes in and Disagreements with Accountants                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | on Accounting and Financial Disclosure                                                                                                                                          | 29     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 9A.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Controls and Procedures                                                                                                                                     | 29     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 9B.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Other Information                                                                                                                                           | 30     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Part III                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 10.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Directors, Executive Officers and Corporate Governance                                                                                                      | 31     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 11.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Executive Compensation                                                                                                                                      | 31     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 12.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Security Ownership of Certain Beneficial Owners and Management and                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Related Stockholder Matters                                                                                                                                                     | 32     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 13.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Certain Relationships and Related Transactions, and Director Independence                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 32     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 14.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Principal Accounting Fees and Services                                                                                                                      | 32     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Part IV                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Item 15.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Exhibits and Financial Statement Schedules                                                                                                                  | 33     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Glossary of Oil and Gas Terms                                                                                                                   | 34                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |   |
| Signatures                                                                                                                                      | 36                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |

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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)                         |   |             | 116,000 |   |         |   | 3,000  |        |   |   | 19,000 |   |   |   | 138,000 |   |
| Gas (Mcf)                          |   |             | 229,000 |   |         |   | 9,000  |        |   |   | 19,000 |   |   |   | 257,000 |   |
| Total (BOE)                        |   |             | 154,000 |   |         |   | 5,000  |        |   |   | 22,000 |   |   |   | 181,000 |   |
|                               |   |             |    |   |         |   |   |        |   |   |   |   |   |   |   |   |
| Standardized measure of discounted |   |             |    |   |         |   |   |        |   |   |   |   |   |   |   |   |
| future net cash flows              |   |             |    |   |         |   |   |        |   |   |   |   |   | $ | 1,923,000 |   |

|       |   | Proved Reserves |    |   |   |   |
|------------|--------|-----------------|---------|--------|--------|--------|
|       |   |            |    |   |   |   |   | Total Oil |   |   | Percent of |   |
|       |   | Oil             |    |   | Gas    |   |   | Equivalent |   |   | Total Oil |   |
|       |   | (Bbls)          |    |   | (Mcf)  |   |   | (BOE) |   |   | Equivalent |   |
| Vacuum     |   |            | 53,000  |   |   |   | 30,000 |   |   |   | 58,000 |   |   |   | 32.1 | % |
| Brahaney   |   |            | 22,000  |   |   |   | 9,000 |   |   |   | 24,000 |   |   |   | 13.3 | % |
| Malaga     |   |            | 11,000  |   |   |   | 61,000 |   |   |   | 21,000 |   |   |   | 11.6 | % |
| Big Spring |   |            | 16,000  |   |   |   | 12,000 |   |   |   | 18,000 |   |   |   | 9.9 | % |
| Petrox     |   |            | 18,000  |   |   |   | - |   |   |   | 18,000 |   |   |   | 9.9 | % |
| Other      |   |            | 18,000  |   |   |   | 145,000 |   |   |   | 42,000 |   |   |   | 23.2 | % |
| Total      |   |            | 138,000 |   |   |   | 257,000 |   |   |   | 181,000 |   |   |   | 100.0 | % |

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Item 

Item 

----

| 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 2009   |   |         | -      |   |          | $      | - |   |
| February 2009  |   |         | -      |   |          |   | - |   |
| March 2009     |   |         | 4.0    |   |          |   | 79.50 |   |
| April 2009     |   |         | -      |   |          |   | - |   |
| May 2009       |   |         | -      |   |          |   | - |   |
| June 2009      |   |         | 35.0   |   |          |   | 79.50 |   |
| July 2009      |   |         | -      |   |          |   | - |   |
| August 2009    |   |         | -      |   |          |   | - |   |
| September 2009 |   |         | 34.0   |   |          |   | 79.50 |   |
| October 2009   |   |         | -      |   |          |   | - |   |
| November 2009  |   |         | -      |   |          |   | - |   |
| December 2009  |   |         | 46.0   |   |          |   | 79.50 |   |
| TOTALS         |   |         | 119.0  |   |          | $      | 79.50 |   |

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Item 

|                           |   | Years ended December 31, |    |
|--------------------------------|--------|--------------------------|---------|
|                           |   | 2009                     |    |   | 2008 |   |   | 2007 |   |   | 2006 |   |   | 2005 |   |
| Revenues                       |   | $                        | 595,229 |   |   | $ | 1,405,115 |   |   | $ | 1,046,768 |   |   | $ | 993,877 |   |   | $ | 850,896 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net income                     |   |                     | 437,734 |   |   |   | 1,255,360 |   |   |   | 890,722 |   |   |   | 862,426 |   |   |   | 735,523 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Partners' share of net income: |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| General partners               |   |                     | 46,435  |   |   |   | 128,009 |   |   |   | 91,521 |   |   |   | 88,248 |   |   |   | 75,335 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Limited partners               |   |                     | 391,299 |   |   |   | 1,127,351 |   |   |   | 799,201 |   |   |   | 774,178 |   |   |   | 660,188 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Limited partners'              |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| net income per unit            |   |                     | 35.00   |   |   |   | 100.83 |   |   |   | 71.48 |   |   |   | 69.24 |   |   |   | 59.05 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Limited partners' cash         |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| distributions per unit         |   |                     | 32.33   |   |   |   | 113.57 |   |   |   | 70.40 |   |   |   | 70.79 |   |   |   | 58.36 |   |
|                           |   |                     |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Total assets                   |   | $                        | 541,245 |   |   | $ | 525,393 |   |   | $ | 692,176 |   |   | $ | 646,071 |   |   | $ | 543,699 |   |

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Item 

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|                                      |   | Year Ended December 31, |    |
|-------------------------------------------|--------|-------------------------|---------|
|                                      |   | 2009                    |    |   | 2008 |   |   | 2007 |   |
| Oil production in barrels                 |   |                    | 16,891  |   |   |   | 17,592 |   |   |   | 18,366 |   |
| Gas production in mcf                     |   |                    | 46,366  |   |   |   | 47,179 |   |   |   | 54,506 |   |
| Total (BOE)                               |   |                    | 24,619  |   |   |   | 25,455 |   |   |   | 27,450 |   |
| Average price per barrel of oil           |   | $                       | 56.61   |   |   | $ | 99.51 |   |   | $ | 71.09 |   |
| Average price per mcf of gas              |   | $                       | 4.30    |   |   | $ | 9.02 |   |   | $ | 7.09 |   |
| Partnership distributions                 |   | $                       | 403,075 |   |   | $ | 1,412,054 |   |   | $ | 875,576 |   |
| Limited partner distributions             |   | $                       | 361,525 |   |   | $ | 1,269,785 |   |   | $ | 787,127 |   |
| Per unit distribution to limited partners |   | $                       | 32.33   |   |   | $ | 113.57 |   |   | $ | 70.40 |   |
| Number of limited partner units           |   |                    | 11,181  |   |   |   | 11,181 |   |   |   | 11,181 |   |

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|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   | Page   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|--------|
| Report of Independent Registered Public Accounting Firm                                                                                                    |   | 17     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Balance Sheets                                                                                                                                             |   | 18     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Statements of Operations                                                                                                                                   |   | 19     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Statements of Changes in Partners' Equity (Deficit)                                                                                                        |   | 20     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Statements of Cash Flows                                                                                                                                   |   | 21     |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |   |   |
| Notes to Financial Statements                                                                                                                              |   | 22     |

----

REPORT 

----

Southwest 

|                                       |   | December 31, |      |
|--------------------------------------------|--------|--------------|-----------|
|                                       |   | 2009         |      |   | 2008 |   |
| Assets                                     |   |         |      |   |   |   |
|                                       |   |         |      |   |   |   |
| Current assets:                            |   |         |      |   |   |   |
| Cash and cash equivalents                  |   | $            | 70,408    |   |   | $ | 75,536 |   |
| Receivable from Managing General Partner   |   |         | 142,150   |   |   |   | 72,678 |   |
| New Mexico income tax deposits             |   |         | 69,965    |   |   |   | 52,740 |   |
| Total current assets                       |   |         | 282,523   |   |   |   | 200,954 |   |
|                                       |   |         |      |   |   |   |   |   |
| Oil and gas properties - using the full-   |   |         |      |   |   |   |   |   |
| cost method of accounting                  |   |         | 3,989,207 |   |   |   | 4,028,306 |   |
| Less accumulated depreciation,             |   |         |      |   |   |   |   |   |
| depletion and amortization                 |   |         | 3,730,485 |   |   |   | 3,703,867 |   |
|                                       |   |         |      |   |   |   |   |   |
| Net oil and gas properties                 |   |         | 258,722   |   |   |   | 324,439 |   |
|                                       |   |         |      |   |   |   |   |   |
|                                       |   | $            | 541,245   |   |   | $ | 525,393 |   |
|                                       |   |         |      |   |   |   |   |   |
| Liabilities and Partners' Equity (Deficit) |   |         |      |   |   |   |   |   |
|                                       |   |         |      |   |   |   |   |   |
| Asset retirement obligation                |   | $            | 360,540   |   |   | $ | 379,347 |   |
|                                       |   |         |      |   |   |   |   |   |
| Partners' equity (deficit):                |   |         |      |   |   |   |   |   |
| General partners                           |   |         | (51,281   | ) |   |   | (56,166 | ) |
| Limited partners                           |   |         | 231,986   |   |   |   | 202,212 |   |
|                                       |   |         |      |   |   |   |   |   |
| Total partners' equity                     |   |         | 180,705   |   |   |   | 146,046 |   |
|                                       |   |         |      |   |   |   |   |   |
|                                       |   | $            | 541,245   |   |   | $ | 525,393 |   |

----

Southwest 

|                                     |   | Years ended December 31, |    |
|------------------------------------------|--------|--------------------------|---------|
|                                     |   | 2009                     |    |   | 2008 |   |   | 2007 |   |
|                                     |   |                     |    |   |   |   |   |   |   |
| Revenues                                 |   |                     |    |   |   |   |   |   |   |
|                                     |   |                     |    |   |   |   |   |   |   |
| Income from net profits interests        |   | $                        | 595,059 |   |   | $ | 1,403,929 |   |   | $ | 1,042,829 |   |
| Interest income                          |   |                     | 170     |   |   |   | 1,186 |   |   |   | 3,939 |   |
|                                     |   |                     | 595,229 |   |   |   | 1,405,115 |   |   |   | 1,046,768 |   |
| Expenses                                 |   |                     |    |   |   |   |   |   |   |   |   |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Depreciation, depletion and amortization |   |                     | 26,618  |   |   |   | 24,729 |   |   |   | 24,484 |   |
| Accretion expense                        |   |                     | 32,647  |   |   |   | 26,398 |   |   |   | 33,434 |   |
| General and administrative               |   |                     | 98,230  |   |   |   | 98,628 |   |   |   | 98,128 |   |
|                                     |   |                     | 157,495 |   |   |   | 149,755 |   |   |   | 156,046 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Net income                               |   | $                        | 437,734 |   |   | $ | 1,255,360 |   |   | $ | 890,722 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Net income allocated to:                 |   |                     |    |   |   |   |   |   |   |   |   |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Managing General Partner                 |   | $                        | 41,791  |   |   | $ | 115,208 |   |   | $ | 82,369 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| General Partner                          |   | $                        | 4,644   |   |   | $ | 12,801 |   |   | $ | 9,152 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Limited partners                         |   | $                        | 391,299 |   |   | $ | 1,127,351 |   |   | $ | 799,201 |   |
|                                     |   |                     |    |   |   |   |   |   |   |   |   |   |
| Per limited partner unit                 |   | $                        | 35.00   |   |   | $ | 100.83 |   |   | $ | 71.48 |   |

----

Southwest 

|                         |   | General  |     |   | Limited  |   |       |   |   |
|------------------------------|--------|----------|----------|--------|----------|--------|------------|--------|--------|
|                         |   | Partners |     |   | Partners |   |       | Total  |   |
| Balance at December 31, 2006 |   | $        | (44,978  | )      |     | $      | 332,572    |   |   | $ | 287,594 |   |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Net income                   |   |     | 91,521   |   |     |   | 799,201    |   |   |   | 890,722 |   |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Distributions                |   |     | (88,449  | )      |     |   | (787,127   | )      |   |   | (875,576 | ) |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Balance at December 31, 2007 |   |     | (41,906  | )      |     |   | 344,646    |   |   |   | 302,740 |   |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Net income                   |   |     | 128,009  |   |     |   | 1,127,351  |   |   |   | 1,255,360 |   |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Distributions                |   |     | (142,269 | )      |     |   | (1,269,785 | )      |   |   | (1,412,054 | ) |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Balance at December 31, 2008 |   |     | (56,166  | )      |     |   | 202,212    |   |   |   | 146,046 |   |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Net income                   |   |     | 46,435   |   |     |   | 391,299    |   |   |   | 437,734 |   |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Distributions                |   |     | (41,550  | )      |     |   | (361,525   | )      |   |   | (403,075 | ) |
|                         |   |     |     |   |     |   |       |   |   |   |   |   |
| Balance at December 31, 2009 |   | $        | (51,281  | )      |     | $      | 231,986    |   |   | $ | 180,705 |   |

----

Southwest 

|                                                 |   | Years ended December 31, |     |
|------------------------------------------------------|--------|--------------------------|----------|
|                                                 |   | 2009                     |     |   | 2008 |   |   | 2007 |   |
| Cash flows from operating activities:                |   |                     |     |   |   |   |   |   |   |
| Cash received from net profits interests             |   | $                        | 496,007  |   |   | $ | 1,513,094 |   |   | $ | 993,557 |   |
| Cash paid for administrative fees and general        |   |                     |     |   |   |   |   |   |   |   |   |   |
| and administrative overhead                          |   |                     | (98,230  | ) |   |   | (98,628 | ) |   |   | (98,128 | ) |
| Interest received                                    |   |                     | 170      |   |   |   | 1,186 |   |   |   | 3,939 |   |
| Other                                                |   |                     | -        |   |   |   | - |   |   |   | 3,456 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net cash provided by operating activities            |   |                     | 397,947  |   |   |   | 1,415,652 |   |   |   | 902,824 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Cash flows used in financing activities:             |   |                     |     |   |   |   |   |   |   |   |   |   |
| Distributions to partners                            |   |                     | (403,075 | ) |   |   | (1,412,054 | ) |   |   | (875,576 | ) |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net (decrease) increase in cash and cash equivalents |   |                     | (5,128   | ) |   |   | 3,598 |   |   |   | 27,248 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Beginning of year                                    |   |                     | 75,536   |   |   |   | 71,938 |   |   |   | 44,690 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| End of year                                          |   | $                        | 70,408   |   |   | $ | 75,536 |   |   | $ | 71,938 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Reconciliation of net income to net cash             |   |                     |     |   |   |   |   |   |   |   |   |   |
| provided by operating activities:               |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net income                                           |   | $                        | 437,734  |   |   | $ | 1,255,360 |   |   | $ | 890,722 |   |
|  Adjustments to reconcile net income to net     |   |                     |     |   |   |   |   |   |   |   |   |   |
| cash provided by operating activities:               |   |                     |     |   |   |   |   |   |   |   |   |   |
| Depreciation, depletion and amortization             |   |                     | 26,618   |   |   |   | 24,729 |   |   |   | 24,484 |   |
| Accretion expense                                    |   |                     | 32,647   |   |   |   | 26,398 |   |   |   | 33,434 |   |
| Settlement of asset retirement obligations           |   |                     |     |   |   |   |   |   |   |   |   |   |
| for plugged and abandoned wells                      |   |                     | (12,355  | ) |   |   | (12,693 | ) |   |   | (3,120 | ) |
| (Increase) decrease in receivables and deposits      |   |                     | (86,697  | ) |   |   | 121,858 |   |   |   | (42,696 | ) |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Net cash provided by operating activities            |   | $                        | 397,947  |   |   | $ | 1,415,652 |   |   | $ | 902,824 |   |
|                                                 |   |                     |     |   |   |   |   |   |   |   |   |   |
| Noncash investing and financing activities:          |   |                     |     |   |   |   |   |   |   |   |   |   |
| (Decrease) increase in oil and gas properties -      |   |                     |     |   |   |   |   |   |   |   |   |   |
| Asset retirement obligations                         |   | $                        | (39,099  | ) |   | $ | (23,794 | ) |   | $ | 645 |   |

----

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 of 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 |
|----|--------------------------------------------------------|

----

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

----

|                                                        |   | 2009   |    |   | 2008   |   |
|-------------------------------------------------------------|--------|--------|---------|--------|--------|--------|
| Beginning of year                                           |   | $      | 379,347 |   |   | $      | 389,436 |   |
| Additional abandonment obligations from new wells           |   |   | -       |   |   |   | 120 |   |
| Reduction of obligations due to wells plugged and abandoned |   |   | (12,355 | )      |   |   | (12,693 | ) |
| Accretion expense                                           |   |   | 32,647  |   |   |   | 26,398 |   |
| Revisions of previous estimates                             |   |   | (39,099 | )      |   |   | (23,914 | ) |
| End of year                                                 |   | $      | 360,540 |   |   | $      | 379,347 |   |

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

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

----

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

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

|                                                    |   | Oil (bbls) |    |   | Gas (mcf) |   |
|---------------------------------------------------------|--------|------------|---------|--------|-----------|--------|
| Total Proved -                                          |   |       |    |   |      |   |
| January 1, 2007                                         |   |       | 193,000 |   |      |   | 506,000 |   |
|                                                    |   |       |    |   |      |   |   |   |
| Revisions of previous estimates                         |   |       | 59,000  |   |      |   | 157,000 |   |
| Production                                              |   |       | (18,000 | )      |      |   | (55,000 | ) |
| December 31, 2007                                       |   |       | 234,000 |   |      |   | 608,000 |   |
|                                                    |   |       |    |   |      |   |   |   |
| Revisions of previous estimates                         |   |       | (93,000 | )      |      |   | (187,000 | ) |
| Production                                              |   |       | (18,000 | )      |      |   | (47,000 | ) |
| December 31, 2008                                       |   |       | 123,000 |   |      |   | 374,000 |   |
|                                                    |   |       |    |   |      |   |   |   |
|     Revisions of previous estimates |   |       | 32,000  |   |      |   | (71,000 | ) |
| Production                                              |   |       | (17,000 | )      |      |   | (46,000 | ) |
| December 31, 2009                                       |   |       | 138,000 |   |      |   | 257,000 |   |
|                                                    |   |       |    |   |      |   |   |   |

----

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

| Proved developed reserves - |   |   |    |   |   |   |
|-----------------------------|--------|--------|---------|--------|--------|--------|
| December 31, 2007           |   |   | 207,000 |   |   |   | 483,000 |   |
| December 31, 2008           |   |   | 104,000 |   |   |   | 276,000 |   |
| December 31, 2009           |   |   | 119,000 |   |   |   | 238,000 |   |

----

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

|                                          |   | 2009   |      |   | 2008   |   |      | 2007   |   |
|-----------------------------------------------|--------|--------|-----------|--------|--------|--------|-----------|--------|--------|
| Future cash inflows                           |   | $      | 8,438,000 |   |   | $      | 7,518,000 |   |   | $ | 25,822,000 |   |
| Production, development and abandonment costs |   |   | 5,544,000 |   |   |   | 4,570,000 |   |   |   | 9,913,000 |   |
| Future net cash flows                         |   |   | 2,894,000 |   |   |   | 2,948,000 |   |   |   | 15,909,000 |   |
| 10% annual discount for                       |   |   |      |   |   |   |      |   |   |   |   |   |
| estimated timing of cash flows                |   |   | 971,000   |   |   |   | 1,054,000 |   |   |   | 7,310,000 |   |
| Standardized measure of                       |   |   |      |   |   |   |      |   |   |   |   |   |
| discounted future net cash flows              |   | $      | 1,923,000 |   |   | $      | 1,894,000 |   |   | $ | 8,599,000 |   |

|                                                   |   | 2009   |      |   | 2008   |   |       | 2007   |   |
|--------------------------------------------------------|--------|--------|-----------|--------|--------|--------|------------|--------|--------|
| Sales of oil and gas produced, net of production costs |   | $      | (595,000  | )      |   | $      | (1,404,000 | )      |   | $ | (1,043,000 | ) |
| Changes in prices and production costs                 |   |   | 132,000   |   |   |   | (5,781,000 | )      |   |   | 3,017,000 |   |
| Changes of production rates (timing) and others        |   |   | 88,000    |   |   |   | 889,000    |   |   |   | (272,000 | ) |
| Revisions of previous quantities estimates             |   |   | 215,000   |   |   |   | (1,269,000 | )      |   |   | 2,184,000 |   |
| Accretion of discount                                  |   |   | 189,000   |   |   |   | 860,000    |   |   |   | 428,000 |   |
| Discounted future net cash flows -                     |   |   |      |   |   |   |       |   |   |   |   |   |
| Beginning of year                                      |   |   | 1,894,000 |   |   |   | 8,599,000  |   |   |   | 4,285,000 |   |
|                                                   |   |   |      |   |   |   |       |   |   |   |   |   |
| End of year                                            |   | $      | 1,923,000 |   |   | $      | 1,894,000  |   |   | $ | 8,599,000 |   |

| 7. | Selected Quarterly Financial Results – (unaudited) |
|----|----------------------------------------------------------|

|                  |   | Quarter |   |
|-----------------------|--------|---------|--------|
|                  |   | First   |   |   | Second |   |   | Third |   |   | Fourth |   |
| 2009:                 |   |    |   |   |   |   |   |   |   |   |   |   |
| Total revenues        |   | $       | 39,137 |   |   | $ | 151,489 |   |   | $ | 199,460 |   |   | $ | 205,143 |   |
| Total expenses        |   |    | 46,969 |   |   |   | 38,245 |   |   |   | 39,712 |   |   |   | 32,569 |   |
| Net (loss) income     |   | $       | (7,832 | ) |   | $ | 113,244 |   |   | $ | 159,748 |   |   | $ | 172,574 |   |
|                  |   |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net (loss) income per |   |    |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| limited partners unit |   | $       | (0.71  | ) |   | $ | 9.06 |   |   | $ | 12.80 |   |   | $ | 13.85 |   |

|                                 |   | Quarter |    |
|--------------------------------------|--------|---------|---------|
|                                 |   | First   |    |   | Second |   |   | Third |   |   | Fourth |   |
| 2008:                                |   |    |    |   |   |   |   |   |   |   |   |   |
| Total revenues                       |   | $       | 414,540 |   |   | $ | 480,670 |   |   | $ | 472,726 |   |   | $ | 37,179 |   |
| Total expenses                       |   |    | 35,994  |   |   |   | 40,107 |   |   |   | 37,873 |   |   |   | 35,781 |   |
| Net income                           |   | $       | 378,546 |   |   | $ | 440,563 |   |   | $ | 434,853 |   |   | $ | 1,398 |   |
|                                 |   |    |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net income per limited partners unit |   | $       | 30.42   |   |   | $ | 35.42 |   |   | $ | 34.95 |   |   | $ | .04 |   |

----

Item 

Item 

----

Item 

----

Item 

Item 

----

Item 

Item 

Item 

| For the Year Ended December 31, |   | 2009   |   |   | 2008   |   |
|---------------------------------|--------|--------|--------|--------|--------|--------|
| Audit Fees                      |   | $      | 17,163 |   |   | $      | 18,030 |   |
| Audit Related Fees              |   |   | -      |   |   |   | - |   |
| Tax Fees                        |   |   | -      |   |   |   | - |   |
| All Other Fees                  |   |   | -      |   |   |   | - |   |
|                            |   |   |   |   |   |   |   |   |
| TOTAL                           |   | $      | 17,163 |   |   | $      | 18,030 |   |

----

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 (Deficit)                                                                                                                                                  |
|   |   | 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 Royalties Institutional 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 Royalties Institutional 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 Royalties Institutional Income Fund |
|--------|-----------------------------------------------|
|   | X-B, L.P., a Delaware limited partnership     |
|   |                                          |
| By:    | Southwest Royalties, Inc., Managing           |
|   | General Partner                               |
|   |                                          |
|   |                                          |
| By:    | /s/ L. Paul Latham                            |
|   | L. Paul Latham                                |
|   | President and Chief Executive Officer         |
|   |                                          |
| Date:  | March 31, 2010                                |

|                                                                                  |   |                                                                                  |
|---------------------------------------------------------------------------------------|--------|---------------------------------------------------------------------------------------|
| /s/ Clayton W Williams                                                                |   | /s/ L. Paul Latham                                                                    |
| Clayton W. Williams, Chairman of the Board                                            |   | L. Paul Latham, President and a Director                                              |
| and a Director                                                                        |   |                                                                                  |
|                                                                                  |   |                                                                                  |
| Date:           March 31, 2010 |   | Date:           March 31, 2010 |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |
| /s/ Mel G. Riggs                                                                      |   |                                                                                  |
| Mel G. Riggs, Vice President – Finance,                                         |   |                                                                                  |
| Treasurer and a Director                                                              |   |                                                                                  |
|                                                                                  |   |                                                                                  |
| Date:           March 31, 2010 |   |                                                                                  |
|                                                                                  |   |                                                                                  |
|                                                                                  |   |                                                                                  |