| 21001 | Odyssey Petroleum Corp. | | Oil & Gas Operator | Jun 2011 |
| 21002 | Odyssey Petroleum, Inc. | Overland Park, KS 66282 | Oil & Gas Operator | Apr 2009 |
| 21003 | Oedekoven Amerifields Resources LLC | Sugar Land, TX 77478 | Oil Operator | Apr 2025 |
| 21004 | Oedekoven Water & Hot Oil | Recluse, WY 82725 | Oil & Gas Operator | May 2025 |
| 21005 | Oeth DRLG Co | | Oil Operator | Dec 2018 |
| 21006 | Oex-1 LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Mar 2024 |
| 21007 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 21008 | Off Broadway Mineral Rights LLC | | Oil & Gas Operator | Oct 2024 |
| 21009 | Offield Lease Operations LLC | Wilson, OK 73463 | Oil & Gas Operator | May 2023 |
| 21010 | Offset Oil & Gas | Big Spring, TX 79720 | Oil & Gas Operator | Aug 2003 |
| 21011 | Offshore Group, Inc. The | Houston, TX 77024 | Oil & Gas Operator | Jun 2025 |
| 21012 | Offshore Oil & Gas Inc | Houston, TX 77063 | Oil & Gas Operator | Sep 1994 |
| 21013 | Offshore Shelf LLC | | Oil & Gas Operator | Dec 2007 |
| 21014 | Ofs-Tulsa Corporation | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 1997 |
| 21015 | Oft Inc. | Houston, TX 77079 | Oil & Gas Operator | Jun 2025 |
| 21016 | Og Co., Inc. | Houston, TX 77057 | Oil & Gas Operator | Jun 2025 |
| 21017 | Oga Operating L.L.C. | Midland, TX 79702 | Oil & Gas Operator | Jan 2000 |
| 21018 | Ogden Oil Co., Inc. | | Oil Operator | May 1981 |
| 21019 | Ogden Resources Corporation | Bryan, TX 77802 | Oil & Gas Operator | Jun 2025 |
| 21020 | Ogden Resources, LTD. | Bryan, TX 77802 | Oil & Gas Operator | Feb 2009 |
| 21021 | Ogh Oil Company | | Oil Operator | Sep 1995 |
| 21022 | Ogle Petroleum Inc. | | Oil & Gas Operator | Dec 1989 |
| 21023 | Oglesby Oil Company | | Oil & Gas Operator | Nov 2023 |
| 21024 | Oglesby Prod & Expl Co Inc | | Oil & Gas Operator | Nov 1987 |
| 21025 | Oglesby, Marshall | | Oil Operator | May 1990 |
| 21026 | Ogog Operating, LLC | Dallas, TX 75367 | Oil & Gas Operator | Jun 2025 |
| 21027 | Ogris Operating LLC | | Gas Operator | Mar 2025 |
| 21028 | Ogs Operating Company, Inc. | Midland, TX 79701 | Oil & Gas Operator | Sep 2008 |
| 21029 | Ogx Operating, LLC | Midland, TX 79702 | Oil & Gas Operator | Jun 2025 |
| 21030 | Ogx Resources LLC | Midland, TX 79702 | Oil & Gas Operator | Oct 2011 |
| 21031 | Ohio Energy Assets, Inc. | Laurelville, OH 43135 | Oil & Gas Operator | Dec 2014 |
| 21032 | Ohio Energy Group Inc | Uniontown, OH 44685 | Oil & Gas Operator | Dec 1988 |
| 21033 | Ohio Energy Operators LLC | Colorado Spring, CO 80908 | Oil Operator | Dec 2018 |
| 21034 | Ohio Investment Leas Inc | Danville, OH 43014 | Oil & Gas Operator | Dec 1989 |
| 21035 | Ohio Kentucky Oil Corporation | Lexington, KY 40503 | Oil & Gas Operator | Dec 2023 |
| 21036 | Ohio L & M Company Inc | Marietta, OH 45750 | Oil & Gas Operator | Dec 2008 |
| 21037 | Ohio Natural Fuel Co | Canton, OH 44718 | Oil & Gas Operator | Dec 1985 |
| 21038 | Ohio Oil & Gas | Fowler, OH 44418 | Oil & Gas Operator | Dec 1988 |
| 21039 | Ohio Production Corp | Westerville, OH 43081 | Oil & Gas Operator | Dec 2001 |
| 21040 | Ohio Production* | Newark, OH 43055 | Oil & Gas Operator | Dec 1987 |
| 21041 | Ohio Valley Energy Systems Corp | Austintown, OH 44515 | Oil & Gas Operator | Dec 2024 |
| 21042 | Ohio Valley Energy, Inc | Livermore, KY 42352 | Oil Operator | Dec 2023 |
| 21043 | Ohlhausen Oil Company | Abilene, TX 79608 | Oil & Gas Operator | Jun 2025 |
| 21044 | Oi Auburn, Inc. | Tulsa, OK 74135 | Gas Operator | Dec 2023 |
| 21045 | Oil & Gas Acquisition Group Inc | Austin, TX 78716 | Oil & Gas Operator | May 2003 |
| 21046 | Oil & Gas Development Company | | Oil & Gas Operator | May 1991 |
| 21047 | Oil & Gas Exploration Inc | Cleveland, OK 74020 | Oil & Gas Operator | Aug 2013 |
| 21048 | Oil & Gas MGMT Inc | Mount Pleasant, PA 15666-3304 | Oil & Gas Operator | Dec 2024 |
| 21049 | Oil & Gas Operations | Midland, TX 79706 | Oil & Gas Operator | Jun 2025 |
| 21050 | Oil & Gas Producers, Inc. | Topeka, KS 66604 | Oil Operator | Jun 2004 |
| 21051 | Oil & Gas Properties | Midland, TX 79704 | Oil & Gas Operator | Jun 2025 |
| 21052 | Oil & Gas Property MGMT., Inc. | Dallas, TX 75201 | Oil & Gas Operator | Jul 1996 |
| 21053 | Oil & Gas Servic | | Oil Operator | Jun 1983 |
| 21054 | Oil & Gas Solutions LTD | Wooster, OH 44691 | Oil & Gas Operator | Dec 2007 |
| 21055 | Oil & Gas SVC Inc | Reelsville, IN 46171-9686 | Gas Operator | Dec 1991 |
| 21056 | Oil & Gas Unlimited Inc | | Oil & Gas Operator | May 2013 |
| 21057 | Oil & Realty Devlop Inc | Columbus, OH 43212 | Oil Operator | Dec 1986 |
| 21058 | Oil And Gas Futures, Inc. | | Oil & Gas Operator | May 1977 |
| 21059 | Oil Capital Corporation | Littleton, CO 80122 | Gas Operator | May 2009 |
| 21060 | Oil Center Operating Inc | Fort Worth, TX 76102-5108 | Oil & Gas Operator | Apr 2014 |
| 21061 | Oil Coast Corp. | S Houston, TX 77587 | Oil & Gas Operator | Jun 2025 |
| 21062 | Oil Company Of America, Inc. | Hays, KS 67601 | Oil Operator | Dec 2009 |
| 21063 | Oil Country Management, Inc. | | Oil & Gas Operator | Jan 2005 |
| 21064 | Oil Creek Production Company | Prague, OK 74864-0667 | Oil & Gas Operator | Feb 2025 |
| 21065 | Oil Development Co | | Oil & Gas Operator | Jan 1979 |
| 21066 | Oil Drillers & D | | Oil & Gas Operator | Feb 1992 |
| 21067 | Oil Enterprises | Logan, OH 43138 | Oil & Gas Operator | Dec 2024 |
| 21068 | Oil Equipment As | | Gas Operator | Jun 1989 |
| 21069 | Oil Exploration Of America Inc | Sisseton, SD 57262-9503 | Oil & Gas Operator | Jun 2001 |
| 21070 | Oil Field Manage | | Oil Operator | Jun 1991 |
| 21071 | Oil Gas Management, Inc. | Kansas City, MO 64106 | Oil Operator | Apr 2011 |
| 21072 | Oil Inc | | Oil & Gas Operator | Dec 1971 |
| 21073 | Oil Internationa | | Oil Operator | Jun 1986 |
| 21074 | Oil Investors Inc | Crescent, OK 73028 | Oil & Gas Operator | Apr 2025 |
| 21075 | Oil Lease Operating Co. | Coldspring, TX 77331 | Oil & Gas Operator | Aug 2003 |
| 21076 | Oil Lift, Incorporated | Metairie, LA 70002 | Oil & Gas Operator | Apr 2020 |
| 21077 | Oil Management Corporation | Dallas, TX 75206 | Oil & Gas Operator | Apr 2022 |
| 21078 | Oil Mountain Energy Inc | Casper, WY 82609 | Oil Operator | Apr 2025 |
| 21079 | Oil Operations Inc | | Oil & Gas Operator | Apr 2011 |
| 21080 | Oil Operators Inc. | | Oil & Gas Operator | Nov 2024 |
| 21081 | Oil Palace, Inc. | | Oil Operator | Jun 2016 |
| 21082 | Oil Partners | Salina, KS 67401 | Oil Operator | Jun 2001 |
| 21083 | Oil Partners, LLC | Salina, KS 67401 | Oil Operator | Feb 2025 |
| 21084 | Oil Patch Energy LLC | Broken Arrow, OK 74014 | Oil & Gas Operator | Jan 2025 |
| 21085 | Oil Patch Operators Co., L.L.C. | Kilgore, TX 75663 | Oil & Gas Operator | Jun 2025 |
| 21086 | Oil Patch Operators, LLC | | Oil & Gas Operator | Jul 2005 |
| 21087 | Oil Pool Inc | Tulsa, OK 74132-2659 | Oil & Gas Operator | Mar 2025 |
| 21088 | Oil Producers In | | Oil & Gas Operator | Dec 1996 |
| 21089 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Jun 2025 |
| 21090 | Oil Production Management Inc | Squaw Valley, CA 93675-9725 | Oil & Gas Operator | Dec 2002 |
| 21091 | Oil Production S | | Oil Operator | Sep 1993 |
| 21092 | Oil Production Systems Inc | Cushing, OK 74023 | Oil & Gas Operator | Jan 2013 |
| 21093 | Oil Projects, LLC | Houston, TX 77027 | Oil & Gas Operator | Jun 2025 |
| 21094 | Oil Prop Company | | Oil & Gas Operator | Sep 1995 |
| 21095 | Oil Prop Investm | | Oil Operator | Dec 1995 |
| 21096 | Oil Properties Co., Inc. | Wichita, KS 67208 | Gas Operator | Dec 2009 |
| 21097 | Oil Property Man | | Oil & Gas Operator | Jun 1995 |
| 21098 | Oil Property Management, Inc. | Attica, KS 67009 | Oil & Gas Operator | Feb 2021 |
| 21099 | Oil Recovery Systems Inc | Tulsa, OK 74145-4619 | Oil & Gas Operator | Mar 2025 |
| 21100 | Oil Recovery, Inc. | | Oil Operator | Sep 1992 |