| 21001 | Oil Company Of America, Inc. | Hays, KS 67601 | Oil Operator | Dec 2009 |
| 21002 | Oil Country Management, Inc. | | Oil & Gas Operator | Jan 2005 |
| 21003 | Oil Creek Production Company | Prague, OK 74864-0667 | Oil & Gas Operator | Jun 2025 |
| 21004 | Oil Development Co | | Oil & Gas Operator | Jan 1979 |
| 21005 | Oil Drillers & D | | Oil & Gas Operator | Feb 1992 |
| 21006 | Oil Enterprises | Logan, OH 43138 | Oil & Gas Operator | Dec 2024 |
| 21007 | Oil Equipment As | | Gas Operator | Jun 1989 |
| 21008 | Oil Exploration Of America Inc | Sisseton, SD 57262-9503 | Oil & Gas Operator | Jun 2001 |
| 21009 | Oil Field Manage | | Oil Operator | Jun 1991 |
| 21010 | Oil Gas Management, Inc. | Kansas City, MO 64106 | Oil Operator | Apr 2011 |
| 21011 | Oil Inc | | Oil & Gas Operator | Dec 1971 |
| 21012 | Oil Internationa | | Oil Operator | Jun 1986 |
| 21013 | Oil Investors Inc | Crescent, OK 73028 | Oil & Gas Operator | Jul 2025 |
| 21014 | Oil Lease Operating Co. | Coldspring, TX 77331 | Oil & Gas Operator | Aug 2003 |
| 21015 | Oil Lift, Incorporated | Metairie, LA 70002 | Oil & Gas Operator | Apr 2020 |
| 21016 | Oil Management Corporation | Dallas, TX 75206 | Oil & Gas Operator | Apr 2022 |
| 21017 | Oil Mountain Energy Inc | Casper, WY 82609 | Oil Operator | Aug 2025 |
| 21018 | Oil Operations Inc | | Oil & Gas Operator | Apr 2011 |
| 21019 | Oil Operators Inc. | | Oil & Gas Operator | Nov 2024 |
| 21020 | Oil Palace, Inc. | | Oil Operator | Jun 2016 |
| 21021 | Oil Partners | Salina, KS 67401 | Oil Operator | Jun 2001 |
| 21022 | Oil Partners, LLC | Salina, KS 67401 | Oil Operator | Jun 2025 |
| 21023 | Oil Patch Energy LLC | Broken Arrow, OK 74014 | Oil & Gas Operator | Jan 2025 |
| 21024 | Oil Patch Operators Co., L.L.C. | Kilgore, TX 75663 | Oil & Gas Operator | Oct 2025 |
| 21025 | Oil Patch Operators, LLC | | Oil & Gas Operator | Jul 2005 |
| 21026 | Oil Pool Inc | Tulsa, OK 74132-2659 | Oil & Gas Operator | Jun 2025 |
| 21027 | Oil Producers In | | Oil & Gas Operator | Dec 1996 |
| 21028 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Oct 2025 |
| 21029 | Oil Production Management Inc | Squaw Valley, CA 93675-9725 | Oil & Gas Operator | Dec 2002 |
| 21030 | Oil Production S | | Oil Operator | Sep 1993 |
| 21031 | Oil Production Systems Inc | Cushing, OK 74023 | Oil & Gas Operator | Jan 2013 |
| 21032 | Oil Projects, LLC | Houston, TX 77027 | Oil & Gas Operator | Oct 2025 |
| 21033 | Oil Prop Company | | Oil & Gas Operator | Sep 1995 |
| 21034 | Oil Prop Investm | | Oil Operator | Dec 1995 |
| 21035 | Oil Properties Co., Inc. | Wichita, KS 67208 | Gas Operator | Dec 2009 |
| 21036 | Oil Property Man | | Oil & Gas Operator | Jun 1995 |
| 21037 | Oil Property Management, Inc. | Attica, KS 67009 | Oil & Gas Operator | Feb 2021 |
| 21038 | Oil Recovery Systems Inc | Tulsa, OK 74145-4619 | Oil & Gas Operator | Jun 2025 |
| 21039 | Oil Recovery, Inc. | | Oil Operator | Sep 1992 |
| 21040 | Oil Reserves Corp Of America | | Oil & Gas Operator | May 2002 |
| 21041 | Oil Rock Oil Company, Inc. | Elizabeth, WV 26143 | Oil & Gas Operator | Dec 2021 |
| 21042 | Oil Rock Resources, LLC | Weatherford, TX 76088 | Oil & Gas Operator | Jan 2024 |
| 21043 | Oil Search (Alaska), LLC | | Oil & Gas Operator | Aug 2025 |
| 21044 | Oil Search Inc | Brookfield, OH 44403 | Oil & Gas Operator | Dec 2024 |
| 21045 | Oil Securities Inc. | | Gas Operator | Dec 2003 |
| 21046 | Oil State Petroleum Inc | Jennings, OK 74038 | Oil & Gas Operator | Jun 2025 |
| 21047 | Oil Tech Producers Corporation | Moundridge, KS 67107 | Gas Operator | Jun 2025 |
| 21048 | Oil Ventures LTD | | Oil & Gas Operator | Jan 2013 |
| 21049 | Oil Well Buyers Corp. | Houston, TX 77056 | Oil & Gas Operator | Dec 2024 |
| 21050 | Oil Well Management Co. | | Oil & Gas Operator | Dec 1989 |
| 21051 | Oil, Gas, Etc. LLC | Katy, TX 77449 | Oil & Gas Operator | Oct 2025 |
| 21052 | Oil,Gas & Other Minerals, Inc. | | Oil & Gas Operator | Apr 1996 |
| 21053 | Oil-Tech Prod Co | | Oil & Gas Operator | Oct 1992 |
| 21054 | Oil-X Corp., The | FT Stockton, TX 79735 | Oil & Gas Operator | Oct 2025 |
| 21055 | Oilbank Production LLC | Norman, OK 73072 | Oil Operator | Jun 2025 |
| 21056 | Oilcat Production Co Inc | McLeansboro, IL 62859 | Oil Operator | Dec 2023 |
| 21057 | Oilco Energy Inc | Duncan, OK 73533 | Oil & Gas Operator | Mar 2015 |
| 21058 | Oildigger Resources Fund L LLLP | Billings, MT 59101 | Oil & Gas Operator | Aug 2025 |
| 21059 | Oilex Int'L Investments, Inc. | Luling, TX 78648 | Oil & Gas Operator | Oct 2025 |
| 21060 | Oilfield Consultants | | Oil & Gas Operator | Dec 1987 |
| 21061 | Oilfield Management, Inc. (A) | Midland, TX 79702 | Oil & Gas Operator | Oct 2025 |
| 21062 | Oilfield Operating Company | Cushing, OK 74023-1347 | Oil & Gas Operator | Jan 2018 |
| 21063 | Oilfield Research, Inc | | Oil Operator | Dec 2021 |
| 21064 | Oilfield Salvage & Service Company | Littleton, CO 80120 | Oil & Gas Operator | Aug 2025 |
| 21065 | Oilfield Search | | Oil Operator | Mar 1990 |
| 21066 | Oilfield Services And Supply Co. Inc. | | Oil Operator | Sep 1989 |
| 21067 | Oilfield Services, LLC | Winfield, KS 67156 | Oil Operator | Nov 2017 |
| 21068 | Oilfield Truck Service | | Oil Operator | Jun 2014 |
| 21069 | Oilrox Resources LLC | San Antonio, TX 78258 | Oil & Gas Operator | Jul 2025 |
| 21070 | Oilsearch Corporation | Albuquerque, NM 87109 | Oil & Gas Operator | Feb 1994 |
| 21071 | Oiltech Inc | Yuba City, CA 95991 | Oil & Gas Operator | Dec 1984 |
| 21072 | Oiltex, Inc. | Baltimore, MD 21221 | Oil & Gas Operator | Dec 2013 |
| 21073 | Oilton Petroleum Inc | Oilton, OK 74052-0459 | Oil & Gas Operator | Oct 2001 |
| 21074 | Oilton Resources, Inc. | Laredo, TX 78041 | Oil & Gas Operator | Oct 2025 |
| 21075 | Oilwell Acquisition Co. | | Oil & Gas Operator | Jun 1999 |
| 21076 | Oilwell Operator | | Gas Operator | Dec 1994 |
| 21077 | Oilwell Operators, Inc. | Pampa, TX 79066 | Oil & Gas Operator | Oct 2025 |
| 21078 | Oily Dog Operators Texas, LLC | Austin, TX 78746 | Oil Operator | Oct 2025 |
| 21079 | Ojai Oil Company | Camarillo, CA 93012 | Oil & Gas Operator | Jul 2025 |
| 21080 | Ojb, Inc. | Buda, TX 78610 | Oil & Gas Operator | Mar 2013 |
| 21081 | Ojt, LLC | Richmond, TX 77469 | Oil Operator | Oct 2025 |
| 21082 | Ok Arena Operating Company | Oklahoma City, OK 73101 | Oil & Gas Operator | Oct 2025 |
| 21083 | Ok Oil Company, Inc. | Bivins, TX 75555 | Oil & Gas Operator | Feb 2013 |
| 21084 | Ok Operating Co | Midland, TX 79702 | Oil & Gas Operator | Aug 1999 |
| 21085 | Ok-La-Tex Production, Inc. | | Oil & Gas Operator | Jan 1982 |
| 21086 | Okc Energy Corporation | Oklahoma City, OK 73120-3119 | Oil & Gas Operator | Nov 2014 |
| 21087 | Okemah Production Inc | | Oil Operator | Dec 2005 |
| 21088 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2025 |
| 21089 | Okie Oil Inc | Sapulpa, OK 74067-0290 | Oil & Gas Operator | Mar 2011 |
| 21090 | Okie Operating Company, LTD. | Tulsa, OK 74103 | Oil & Gas Operator | Oct 2025 |
| 21091 | Okkatahula, Inc. | | Oil Operator | Nov 1978 |
| 21092 | Okla Sub-Surface Pump & Supply Co | Seminole, OK 74804 | Oil & Gas Operator | Sep 2024 |
| 21093 | Okla. Magic Circle Energy Corp. | Shawnee, OK 74801 | Oil & Gas Operator | Jul 2004 |
| 21094 | Oklahoma Arrowhead Energy, Inc. | Nichols Hill, OK 73116 | Oil & Gas Operator | Sep 1996 |
| 21095 | Oklahoma Basic Economy Corp | Houston, TX 77002-6003 | Oil & Gas Operator | Apr 2020 |
| 21096 | Oklahoma Cellulose Inc | Cleveland, OK 74020 | Oil Operator | Jun 2025 |
| 21097 | Oklahoma Crude Inc | Morris, OK 74445 | Oil & Gas Operator | Apr 2024 |
| 21098 | Oklahoma Crude Reclaimers, LLC | | Oil Operator | Jul 2025 |
| 21099 | Oklahoma Ea II, L.L.C. | Oklahoma City, OK 73102 | Oil & Gas Operator | Dec 2004 |
| 21100 | Oklahoma Energy & Exploration, Inc. | Tulsa, OK 74114 | Oil Operator | Jan 1996 |