EXHIBIT 21 LIST OF SUBSIDIARIES OF HALLWOOD ENERGY PARTNERS, L. P. HEP Operating Partners, L.P., a Delaware limited partnership EDP Operating, Ltd., a Colorado limited partnership SODP, Inc., a Texas corporation Hallwood Oil and Gas, Inc., a California corporation Hallwood Petroleum, Inc., a Delaware corporation Hallwood Consolidated Resources Corporation, a Delaware corporation May Drilling Partnership 1983-1, a Texas general partnership May Drilling Partnership 1983-2, a Texas general partnership May Drilling Partnership 1983-3, a Texas general partnership May Drilling Partnership 1984-1, a Texas general partnership May Drilling Partnership 1984-2, a Texas general partnership May Drilling Partnership 1984-3, a Texas general partnership Hallwood Spraberry Drilling Company, L.L.C., a Colorado limited liability company Hallwood San Juan, L.L.C., a Delaware limited liability company Sunburst Exploration, Inc., a California corporation