| 3301 | O'Brien Energy Company | Shreveport, LA 71136 | Oil & Gas Operator | Sep 2019 |
| 3302 | O'Brien Operating Company | | Oil & Gas Operator | Dec 2004 |
| 3303 | O'Malley Production Co. Inc. | | Oil & Gas Operator | Mar 1988 |
| 3304 | O'Meara LLC | | Oil & Gas Operator | Oct 2022 |
| 3305 | O'Meara, Inc. | | Oil & Gas Operator | Dec 2006 |
| 3306 | O'Sullivan & Scully, Inc. | | Oil & Gas Operator | Oct 1994 |
| 3307 | O'Sullivan Oil & Gas Co., Inc. | Houston, TX 77002 | Oil & Gas Operator | Oct 2000 |
| 3308 | O. B. And Keith Whatley | | Oil Operator | Jul 1993 |
| 3309 | O. B. Beck | | Oil Operator | Feb 1991 |
| 3310 | O. B. Mobley | | Oil & Gas Operator | Jul 1989 |
| 3311 | O. B. Mobley, Et Al | | Oil Operator | Jul 1989 |
| 3312 | O. B. Whatley | | Oil Operator | Jul 1993 |
| 3313 | O. D. Maybrier | | Oil Operator | Dec 2011 |
| 3314 | O. F. H., Inc. | | Oil Operator | May 1990 |
| 3315 | O. G., Inc. | | Oil & Gas Operator | Nov 1992 |
| 3316 | O. O. Cummings | | Gas Operator | Jan 1999 |
| 3317 | O.B. Whatley Oil Company, Inc. | | Oil Operator | Feb 2013 |
| 3318 | O.B., Keith & Owen B. Whatley | | Oil Operator | Jul 1989 |
| 3319 | O.G.P. Operating, Inc. | Dallas, TX 75231 | Oil & Gas Operator | Apr 2025 |
| 3320 | O.I.L. Energy, Inc. | | Oil & Gas Operator | Dec 1984 |
| 3321 | Oak Energy, LLC | Houston, TX 77027 | Oil & Gas Operator | Apr 2025 |
| 3322 | Oak Valley Operating, LLC | The Woodlands, TX 77380 | Oil & Gas Operator | Jun 2015 |
| 3323 | Oakfield Energy LLC | | Oil Operator | Jun 2019 |
| 3324 | Oakland Corporation | | Oil & Gas Operator | Dec 1981 |
| 3325 | Oakley Oil & Gas, L.L.C. | | Oil & Gas Operator | Mar 2012 |
| 3326 | Oasis Production Co., Inc. | | Oil & Gas Operator | Jun 1988 |
| 3327 | Occ Operating Co. | | Oil & Gas Operator | Apr 2019 |
| 3328 | Occidental Energy Company, Inc. | Houston, TX 77282 | Oil & Gas Operator | Jul 2021 |
| 3329 | Ocean Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 3330 | Octagon Resources Corporation | | Oil Operator | Apr 2005 |
| 3331 | Ody Oil Corp. | | Oil & Gas Operator | Oct 1994 |
| 3332 | Odyssey Operating Company | | Oil & Gas Operator | Sep 2020 |
| 3333 | Offshore Oil & Gas Inc | Houston, TX 77063 | Oil & Gas Operator | Sep 1994 |
| 3334 | Offshore Shelf LLC | | Oil & Gas Operator | Dec 2007 |
| 3335 | Oil & Gas Development Company | | Oil & Gas Operator | May 1991 |
| 3336 | Oil & Gas Producers, Inc. | Topeka, KS 66604 | Oil Operator | Jun 2004 |
| 3337 | Oil & Gas Property MGMT., Inc. | Dallas, TX 75201 | Oil & Gas Operator | Jul 1996 |
| 3338 | Oil And Gas Futures, Inc. | | Oil & Gas Operator | May 1977 |
| 3339 | Oil Country Management, Inc. | | Oil & Gas Operator | Jan 2005 |
| 3340 | Oil Lift, Incorporated | Metairie, LA 70002 | Oil & Gas Operator | Apr 2020 |
| 3341 | Oil Palace, Inc. | | Oil Operator | Jun 2016 |
| 3342 | Oil Patch Operators, LLC | | Oil & Gas Operator | Jul 2005 |
| 3343 | Oil Recovery, Inc. | | Oil Operator | Sep 1992 |
| 3344 | Oil Reserves Corp Of America | | Oil & Gas Operator | May 2002 |
| 3345 | Oil Well Buyers Corp. | Houston, TX 77056 | Oil & Gas Operator | Dec 2024 |
| 3346 | Oil,Gas & Other Minerals, Inc. | | Oil & Gas Operator | Apr 1996 |
| 3347 | Oilwell Acquisition Co. | | Oil & Gas Operator | Jun 1999 |
| 3348 | Ok Oil Company, Inc. | Bivins, TX 75555 | Oil & Gas Operator | Feb 2013 |
| 3349 | Ok-La-Tex Production, Inc. | | Oil & Gas Operator | Jan 1982 |
| 3350 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jan 2025 |
| 3351 | Okie Operating Company, LTD. | Tulsa, OK 74103 | Oil & Gas Operator | Apr 2025 |
| 3352 | Okkatahula, Inc. | | Oil Operator | Nov 1978 |
| 3353 | Oldfield Operating Corporation | | Oil Operator | Dec 2013 |
| 3354 | Oleum Incorporated | | Oil & Gas Operator | Mar 1996 |
| 3355 | Oleum Operating Company, L.C. | Longview, TX 75606 | Oil & Gas Operator | Dec 2021 |
| 3356 | Oleum Operating La LLC | | Oil & Gas Operator | Nov 2022 |
| 3357 | Oliditt Corporation | | Gas Operator | Mar 2022 |
| 3358 | Oliditt Production Inc. | | Gas Operator | Sep 1998 |
| 3359 | Olipdp II, LLC | Lafayette, LA 70503 | Oil & Gas Operator | Apr 2025 |
| 3360 | Olympic Natural Gas Company | | Oil & Gas Operator | Oct 1990 |
| 3361 | Olympic Oil & Gas Co., Inc. | | Oil Operator | Apr 1991 |
| 3362 | Olympic Petroleum Company | Tulsa, OK 74114 | Oil & Gas Operator | Jun 1998 |
| 3363 | Olympic Production Company | | Oil & Gas Operator | Jul 1994 |
| 3364 | Omeara Bros. | | Oil & Gas Operator | Oct 1982 |
| 3365 | Omega Energy Corp. | Graham, TX 76450 | Oil & Gas Operator | Apr 2025 |
| 3366 | Omega Energy Incorporated | | Oil & Gas Operator | May 1998 |
| 3367 | Omni Operating Company | Osage, WY 82723 | Oil & Gas Operator | Sep 2001 |
| 3368 | Onshore Exp Cor-La Nat Res Inc | | Oil & Gas Operator | Oct 1978 |
| 3369 | Onshore Pipeline Const Co Inc | | Oil & Gas Operator | Aug 1998 |
| 3370 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 3371 | Onyx Energy Dev Of Texas Inc. | | Oil Operator | Dec 1996 |
| 3372 | Onyx Energy Of Texas Inc. | | Oil Operator | Dec 1996 |
| 3373 | Onyxx Energy LLC | | Oil & Gas Operator | Mar 2017 |
| 3374 | Opal Oil Inc. | | Oil Operator | Sep 2021 |
| 3375 | Opmi Operating Company | Houston, TX 77057 | Oil & Gas Operator | Jun 2008 |
| 3376 | Ops Group Limited | Houston, TX 77060 | Oil & Gas Operator | Jun 2014 |
| 3377 | Optimistic Oil Co. | | Oil & Gas Operator | Dec 1991 |
| 3378 | Ora Oil Company | | Oil & Gas Operator | May 2017 |
| 3379 | Oracle Oil, LLC | | Oil & Gas Operator | Jul 2013 |
| 3380 | Orb Exploration, L.L.C. | | Oil & Gas Operator | Jun 2017 |
| 3381 | Orion Oil & Gas, LLC | Houston, TX 77042 | Oil & Gas Operator | Oct 2007 |
| 3382 | Orleans Exploration Co., Inc. | | Oil & Gas Operator | Aug 1990 |
| 3383 | Orx Resources, Inc. | | Oil & Gas Operator | Dec 2009 |
| 3384 | Orx Resources, L.L.C. | Houston, TX 77067 | Oil & Gas Operator | Apr 2025 |
| 3385 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 3386 | Osman Global Services LLC | | Oil & Gas Operator | Jan 2025 |
| 3387 | Osr Oil & Gas Corp | Midland, TX 79710 | Oil & Gas Operator | Dec 2024 |
| 3388 | Osyka Permian, LLC | Houston, TX 77079 | Oil & Gas Operator | Apr 2025 |
| 3389 | Otis C. Coles, Jr. | | Oil & Gas Operator | Jan 1998 |
| 3390 | Ouachita Development Corp. | | Gas Operator | Mar 2014 |
| 3391 | Ouida Oil Co. | | Oil & Gas Operator | Apr 1999 |
| 3392 | Output Acquisition Corp. | | Oil & Gas Operator | Jul 2010 |
| 3393 | Owen Production Co | | Oil Operator | May 2001 |
| 3394 | Owl Creek Production Co., Inc. | Houston, TX 77027 | Oil & Gas Operator | Apr 2006 |
| 3395 | Oxbow EP LLC | | Oil Operator | Dec 2024 |
| 3396 | Oxford Exploration Company | Denver, CO 80237 | Oil & Gas Operator | Aug 1995 |
| 3397 | Oxtex Inc | | Oil & Gas Operator | Oct 1989 |
| 3398 | Oxy Petroleum Inc | | Oil & Gas Operator | Jan 1986 |
| 3399 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Apr 2025 |
| 3400 | Ozark Production Company, Inc. | | Oil & Gas Operator | Jan 2025 |