| 1 | H E C I Exploration Company | | Oil & Gas Operator | Dec 1990 |
| 2 | Hal Oil & Gas Co., Inc. | | Oil & Gas Operator | Apr 1993 |
| 3 | Halcon Resources Operating, Inc. | Tulsa, OK 74135 | Oil & Gas Operator | Dec 2013 |
| 4 | Hallwood Petroleum, Inc. | Midland, TX 79701 | Oil & Gas Operator | Jun 2025 |
| 5 | Harbor Operating, LLC | | Oil & Gas Operator | Dec 1999 |
| 6 | Harbor Petroleum, LLC | Granbury, TX 76049 | Oil & Gas Operator | Oct 2025 |
| 7 | Hardy Oil & Gas USA Inc. | Houston, TX 77079 | Oil & Gas Operator | Jun 1996 |
| 8 | Hassie Hunt Expl. Company | | Oil & Gas Operator | Aug 2008 |
| 9 | Headington Oil Company | Dallas, TX 75231 | Oil & Gas Operator | Dec 2016 |
| 10 | Helis Oil & Gas Company, L.L.C. | New Orleans, LA 70130 | Oil & Gas Operator | Oct 2023 |
| 11 | Henderson Pet Corp Of Delaware | | Oil & Gas Operator | Oct 2019 |
| 12 | Henry Production Company, Inc. | Lafayette, LA 70505 | Oil & Gas Operator | Oct 2019 |
| 13 | Hilcorp Energy Company | Houston, TX 77208 | Oil & Gas Operator | Oct 2025 |
| 14 | Hochendel Consultants | | Oil & Gas Operator | Jul 1995 |
| 15 | Home Petroleum Corp | Victoria, TX 77902 | Oil & Gas Operator | Oct 2025 |
| 16 | Homer E. Hines, Inc. | | Oil Operator | Sep 1978 |
| 17 | Houma Operating Company, Inc. | | Oil & Gas Operator | Jun 1998 |
| 18 | Houston Exploration Co, The | Houston, TX 77002 | Oil & Gas Operator | Apr 2017 |
| 19 | Huffco Petroleum Corporation | | Oil & Gas Operator | Jul 1988 |
| 20 | Hughes & Hughes | | Oil & Gas Operator | May 1984 |
| 21 | Hughes Denny Offshore Expl Inc | | Oil & Gas Operator | Nov 1988 |
| 22 | Hughes Eastern Petroleum, LTD. | | Oil & Gas Operator | Jun 1986 |
| 23 | Hughes-Denny Petroleum Co.,Inc | | Oil & Gas Operator | Dec 1987 |
| 24 | Hunt Oil Company | Dallas, TX 75201 | Oil & Gas Operator | Oct 2025 |
| 25 | Hunt Petroleum (Aec), Inc. | Dallas, TX 75201 | Oil & Gas Operator | Nov 2008 |
| 26 | Hunt Petroleum Corporation | Dallas, TX 75201 | Oil & Gas Operator | Nov 2008 |
| 27 | Hydrocarbon MGMT., Inc. | | Oil & Gas Operator | Mar 1997 |