**Exhibit 21**

**SUBSIDIARIES OFTHE REGISTRANT**

·                  Warrior Gas Co.,a Texas corporation, which has a wholly owned subsidiary, Clajon IndustrialGas, Inc., a Texas corporation

·                  Clayton WilliamsTrading Company, a Texas corporation

·                  Clayton WilliamsVenezuela, Inc., a Delaware corporation

·                  CWEIAcquisitions, Inc., a Delaware corporation

·                  Clayton WilliamsPipeline, Inc. (formerly Clayton Williams Midland, Inc.), a Texas corporation

·                  CWEI Romere PassAcquisition Corp., a Delaware corporation, which is the sole member of RomerePass Acquisition, L.L.C. (formerly Romere Pass Acquisition Corp.)

·                  WarriorMississippi Corporation, a Delaware corporation

·                  SouthwestRoyalties, Inc., a Delaware corporation, which has two wholly ownedsubsidiaries, Blue Hill Company, a Delaware corporation and Tex-Hal Partners,Inc., a Delaware corporation

·                  CWEI LongfellowRanch I, L.P., a Texas limited partnership

·                  CWEI SouthLouisiana II, L.P., a Texas limited partnership

·                  Rocky Arroyo,L.P., a Texas limited partnership

·                  CWEI West Pyle/McGonagill,L.P., a Texas limited partnership

·                  CWEI SouthLouisiana III, L.P., a Texas limited partnership

·                  CWEI NorthLouisiana, L.P., a Texas limited partnership

·                  Floyd Prospect,L.P., a Texas limited partnership

·                  SouthwestRoyalties, Inc. Income Fund V, a Tennessee limited partnership

·                  SouthwestRoyalties, Inc. Income Fund VI, a Tennessee limited partnership

·                  Southwest Oiland Gas Income Fund VII-A, L.P., a Delaware limited partnership

·                  SouthwestRoyalties Institutional Income Fund VII-B, L.P., a Delaware limited partnership

·                  SouthwestRoyalties, Inc. Income/Drilling Program 1987-I, L.P., a Delaware limitedpartnership

·                  Southwest Oiland Gas Income Fund VIII-A, L.P., a Delaware limited partnership

·                  SouthwestRoyalties Institutional Income Fund VIII-B, L.P., a Delaware limitedpartnership

·                  SouthwestCombination Income/Drilling Program 1988, L.P., a Delaware limited partnership

·                  Southwest Oiland Gas Income Fund IX-A, L.P., a Delaware limited partnership

·                  SouthwestRoyalties Institutional Income Fund IX-B, L.P., a Delaware limited partnership

·                  SouthwestOil & Gas Income Fund X-A, L.P., a Delaware limited partnership

·                  SouthwestRoyalties Institutional Income Fund X-A, L.P., a Delaware limited partnership

·                  SouthwestOil & Gas Income Fund X-B, L.P., a Delaware limited partnership

·                  SouthwestRoyalties Institutional Income Fund X-B, L.P., a Delaware limited partnership

·                  SouthwestOil & Gas Income Fund X-C, L.P., a Delaware limited partnership

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**SUBSIDIARIES OF THE REGISTRANT**

**(Continued)**

·                  SouthwestRoyalties Institutional Income Fund X-C, L.P., a Delaware limited partnership

·                  SouthwestOil & Gas Income Fund XI-A, L.P., a Delaware limited partnership

·                  SouthwestInstitutional Income Fund XI-A, L.P., a Delaware limited partnership

·                  Southwest DevelopmentalDrilling Fund 1990, L.P., a Delaware limited partnership

·                  SouthwestDevelopmental Drilling Fund 91-A, L.P., a Delaware limited partnership

·                  SouthwestDevelopmental Drilling Fund 92-A, L.P., a Delaware limited partnership

·                  SouthwestDevelopmental Drilling Fund 1993, L.P., a Delaware limited partnership

·                  SouthwestRoyalties Institutional Income Fund XI-B, L.P., a Delaware limited partnership

·                  SouthwestDevelopmental Drilling Fund 1994, L.P., a Delaware limited partnership

·                  Floyd ProspectII, L.P., a Texas limited partnership

·                  West CoastEnergy Properties GP, LLC, a Texas limited liability company

·                  West CoastEnergy Properties, L.P., a Texas limited partnership

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