| 1 | Dalen Resources Oil & Gas Co. | Dallas, TX 75206 | Oil & Gas Operator | Jun 2010 |
| 2 | Delaware Ecco Petroleum Inc. | Rockwall, TX 75087 | Oil & Gas Operator | Jul 2001 |
| 3 | Devon Energy Operating Co., L.P. | Oklahoma City, OK 73102 | Oil & Gas Operator | Jun 2009 |
| 4 | Devon Energy Production Company LP | Oklahoma City, OK 73102 | Oil & Gas Operator | Apr 2024 |
| 5 | Diasu Oil & Gas Co., Inc. | Houston, TX 77002 | Oil & Gas Operator | Mar 2016 |
| 6 | Diversified Production LLC | Minden, LA 71055 | Oil & Gas Operator | Apr 2024 |
| 7 | Dorfman Production Company | Kilgore, TX 75663 | Oil & Gas Operator | Apr 2024 |
| 8 | Douglas Petroleum Inc. | Spring, TX 77379 | Oil & Gas Operator | Nov 2010 |
| 9 | DPMP Energy LLC | Prosper, TX 75078 | Oil & Gas Operator | Dec 2023 |
| 10 | Dynamic Petroleum Res., Inc. | Houston, TX 77068 | Oil & Gas Operator | Jul 1994 |