| 1 | H E C I Exploration Company | | Oil & Gas Operator | Dec 1990 |
| 2 | Hallar Enterprises, Inc. | | Oil Operator | Oct 2007 |
| 3 | Hallwood Petroleum, Inc. | Midland, TX 79701 | Oil & Gas Operator | Apr 2024 |
| 4 | Headington Oil Company | Dallas, TX 75231 | Oil & Gas Operator | Dec 2016 |
| 5 | Headington Oil Company, L.P. | Dallas, TX 75231 | Oil & Gas Operator | Mar 2008 |
| 6 | Hec Petroleum, Inc | Midland, TX 79705 | Oil & Gas Operator | Mar 2006 |
| 7 | Henry Production Company, Inc. | Lafayette, LA 70505 | Oil & Gas Operator | Oct 2019 |
| 8 | Hilcorp Energy Company | Houston, TX 77208 | Oil & Gas Operator | Nov 2024 |
| 9 | Hilliard Petroleum Inc. | Shreveport, LA 71101 | Oil & Gas Operator | Sep 2009 |
| 10 | Holleman & Parks Oil & Gas Inc | | Oil & Gas Operator | May 1995 |
| 11 | Houma Operating Company, Inc. | | Oil & Gas Operator | Jun 1998 |
| 12 | Houston Oil & Minerals Corp. | Houston, TX 77002 | Oil & Gas Operator | Aug 1996 |
| 13 | Houston Oil Fields Company | | Oil & Gas Operator | Apr 1987 |
| 14 | Huffco Petroleum Corporation | | Oil & Gas Operator | Jul 1988 |