| 1 | Dalen Resources Oil & Gas Co. | Dallas, TX 75206 | Oil & Gas Operator | Jun 2010 |
| 2 | Damson Oil Corporation | Houston, TX 77210 | Oil & Gas Operator | Mar 2005 |
| 3 | Dan A. Hughes Company | | Oil & Gas Operator | Dec 2005 |
| 4 | Daniel Oil Company | | Oil & Gas Operator | Jan 1983 |
| 5 | Davis Oil Company | Denver, CO 80202 | Oil & Gas Operator | Jun 1988 |
| 6 | Decker Operating Co., L.L.C. | Houston, TX 77008 | Oil & Gas Operator | Oct 2025 |
| 7 | Denbury Management, Inc. | Dallas, TX 75252 | Oil & Gas Operator | Dec 1999 |
| 8 | Denbury Onshore, LLC | Plano, TX 75024 | Oil & Gas Operator | Oct 2025 |
| 9 | Denbury Resources Inc. | Plano, TX 75024 | Oil & Gas Operator | Dec 2003 |
| 10 | Denex, Inc. | | Oil & Gas Operator | Jul 1983 |
| 11 | Denovo Oil & Gas, Inc. | Houston, TX 77210 | Oil & Gas Operator | May 1995 |
| 12 | Desco Oil Company | Houston, TX 77056 | Oil & Gas Operator | Feb 2017 |
| 13 | Devon Louisiana Corporation | Houston, TX 77002 | Oil & Gas Operator | Oct 2019 |
| 14 | Diasu Oil & Gas Co., Inc. | Houston, TX 77002 | Oil & Gas Operator | Mar 2016 |
| 15 | Dimension Energy Co., L.L.C. | | Oil & Gas Operator | Dec 2024 |
| 16 | Dominion Exploration & Production Inc | Houston, TX 77060 | Oil & Gas Operator | Apr 2015 |
| 17 | Duer Wagner & Company | Fort Worth, TX 76102 | Oil & Gas Operator | Dec 1998 |
| 18 | Dynamic Exploration, Inc. | | Oil & Gas Operator | Oct 2003 |