| 201 | Oil & Gas Unlimited Inc | | Oil & Gas Operator | May 2013 |
| 202 | Oil & Realty Devlop Inc | Columbus, OH 43212 | Oil Operator | Dec 1986 |
| 203 | Oil And Gas Futures, Inc. | | Oil & Gas Operator | May 1977 |
| 204 | Oil Capital Corporation | Littleton, CO 80122 | Gas Operator | May 2009 |
| 205 | Oil Center Operating Inc | Fort Worth, TX 76102-5108 | Oil & Gas Operator | Apr 2014 |
| 206 | Oil Coast Corp. | S Houston, TX 77587 | Oil & Gas Operator | Jun 2025 |
| 207 | Oil Company Of America, Inc. | Hays, KS 67601 | Oil Operator | Dec 2009 |
| 208 | Oil Country Management, Inc. | | Oil & Gas Operator | Jan 2005 |
| 209 | Oil Creek Production Company | Prague, OK 74864-0667 | Oil & Gas Operator | Feb 2025 |
| 210 | Oil Development Co | | Oil & Gas Operator | Jan 1979 |
| 211 | Oil Drillers & D | | Oil & Gas Operator | Feb 1992 |
| 212 | Oil Enterprises | Logan, OH 43138 | Oil & Gas Operator | Dec 2024 |
| 213 | Oil Equipment As | | Gas Operator | Jun 1989 |
| 214 | Oil Exploration Of America Inc | Sisseton, SD 57262-9503 | Oil & Gas Operator | Jun 2001 |
| 215 | Oil Field Manage | | Oil Operator | Jun 1991 |
| 216 | Oil Field Production Inc | Tulsa, OK 74133 | Oil Operator | Feb 2025 |
| 217 | Oil Gas Management, Inc. | Kansas City, MO 64106 | Oil Operator | Apr 2011 |
| 218 | Oil Inc | | Oil & Gas Operator | Dec 1971 |
| 219 | Oil Internationa | | Oil Operator | Jun 1986 |
| 220 | Oil Investors Inc | Crescent, OK 73028 | Oil & Gas Operator | Mar 2025 |
| 221 | Oil Lease Operating Co. | Coldspring, TX 77331 | Oil & Gas Operator | Aug 2003 |
| 222 | Oil Lift, Incorporated | Metairie, LA 70002 | Oil & Gas Operator | Apr 2020 |
| 223 | Oil Management Corporation | Dallas, TX 75206 | Oil & Gas Operator | Apr 2022 |
| 224 | Oil Mountain Energy Inc | Casper, WY 82609 | Oil Operator | Apr 2025 |
| 225 | Oil Operations Inc | | Oil & Gas Operator | Apr 2011 |
| 226 | Oil Operators Inc. | | Oil & Gas Operator | Nov 2024 |
| 227 | Oil Palace, Inc. | | Oil Operator | Jun 2016 |
| 228 | Oil Partners | Salina, KS 67401 | Oil Operator | Jun 2001 |
| 229 | Oil Partners, LLC | Salina, KS 67401 | Oil Operator | Feb 2025 |
| 230 | Oil Patch Energy LLC | Broken Arrow, OK 74014 | Oil & Gas Operator | Jan 2025 |
| 231 | Oil Patch Operators Co., L.L.C. | Kilgore, TX 75663 | Oil & Gas Operator | Jun 2025 |
| 232 | Oil Patch Operators, LLC | | Oil & Gas Operator | Jul 2005 |
| 233 | Oil Pool Inc | Tulsa, OK 74132-2659 | Oil & Gas Operator | Jan 2025 |
| 234 | Oil Producers In | | Oil & Gas Operator | Dec 1996 |
| 235 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Jun 2025 |
| 236 | Oil Production Management Inc | Squaw Valley, CA 93675-9725 | Oil & Gas Operator | Dec 2002 |
| 237 | Oil Production S | | Oil Operator | Sep 1993 |
| 238 | Oil Production Systems Inc | Cushing, OK 74023 | Oil & Gas Operator | Jan 2013 |
| 239 | Oil Projects, LLC | Houston, TX 77027 | Oil & Gas Operator | Jun 2025 |
| 240 | Oil Prop Company | | Oil & Gas Operator | Sep 1995 |
| 241 | Oil Prop Investm | | Oil Operator | Dec 1995 |
| 242 | Oil Properties Co., Inc. | Wichita, KS 67208 | Gas Operator | Dec 2009 |
| 243 | Oil Property Man | | Oil & Gas Operator | Jun 1995 |
| 244 | Oil Property Management, Inc. | Attica, KS 67009 | Oil & Gas Operator | Feb 2021 |
| 245 | Oil Recovery Systems Inc | Tulsa, OK 74145-4619 | Oil & Gas Operator | Feb 2025 |
| 246 | Oil Recovery, Inc. | | Oil Operator | Sep 1992 |
| 247 | Oil Reserves Corp Of America | | Oil & Gas Operator | May 2002 |
| 248 | Oil Rock Energy Inc. / O.R.E. | Dallas, TX 75208 | Oil & Gas Operator | Jun 2025 |
| 249 | Oil Rock Oil Company, Inc. | Elizabeth, WV 26143 | Oil & Gas Operator | Dec 2021 |
| 250 | Oil Rock Resources, LLC | Weatherford, TX 76088 | Oil & Gas Operator | Jan 2024 |
| 251 | Oil Search (Alaska), LLC | | Oil & Gas Operator | Apr 2025 |
| 252 | Oil Search Inc | Brookfield, OH 44403 | Oil & Gas Operator | Dec 2024 |
| 253 | Oil Securities Inc. | | Gas Operator | Dec 2003 |
| 254 | Oil State Petroleum Inc | Jennings, OK 74038 | Oil & Gas Operator | Jan 2025 |
| 255 | Oil Tech Producers Corporation | Moundridge, KS 67107 | Gas Operator | Feb 2025 |
| 256 | Oil Ventures LTD | | Oil & Gas Operator | Jan 2013 |
| 257 | Oil Well Buyers Corp. | Houston, TX 77056 | Oil & Gas Operator | Dec 2024 |
| 258 | Oil Well Management Co. | | Oil & Gas Operator | Dec 1989 |
| 259 | Oil, Gas, Etc. LLC | Katy, TX 77449 | Oil & Gas Operator | Jun 2025 |
| 260 | Oil,Gas & Other Minerals, Inc. | | Oil & Gas Operator | Apr 1996 |
| 261 | Oil-Tech Prod Co | | Oil & Gas Operator | Oct 1992 |
| 262 | Oil-X Corp., The | FT Stockton, TX 79735 | Oil & Gas Operator | Jun 2025 |
| 263 | Oilbank Production LLC | Norman, OK 73072 | Oil Operator | Feb 2025 |
| 264 | Oilcat Production Co Inc | McLeansboro, IL 62859 | Oil Operator | Dec 2023 |
| 265 | Oilco Energy Inc | Duncan, OK 73533 | Oil & Gas Operator | Mar 2015 |
| 266 | Oildigger Resources Fund L LLLP | Billings, MT 59101 | Oil & Gas Operator | Apr 2025 |
| 267 | Oilex Int'L Investments, Inc. | Luling, TX 78648 | Oil & Gas Operator | Jun 2025 |
| 268 | Oilfield Consultants | | Oil & Gas Operator | Dec 1987 |
| 269 | Oilfield Management, Inc. (A) | Midland, TX 79702 | Oil & Gas Operator | Jun 2025 |
| 270 | Oilfield Operating Company | Cushing, OK 74023-1347 | Oil & Gas Operator | Jan 2018 |
| 271 | Oilfield Research, Inc | | Oil Operator | Dec 2021 |
| 272 | Oilfield Salvage & Service Company | Littleton, CO 80120 | Oil & Gas Operator | Apr 2025 |
| 273 | Oilfield Search | | Oil Operator | Mar 1990 |
| 274 | Oilfield Services And Supply Co. Inc. | | Oil Operator | Sep 1989 |
| 275 | Oilfield Services, LLC | Winfield, KS 67156 | Oil Operator | Nov 2017 |
| 276 | Oilfield Truck Service | | Oil Operator | Jun 2014 |
| 277 | Oilrox Resources LLC | San Antonio, TX 78258 | Oil & Gas Operator | Mar 2025 |
| 278 | Oilsearch Corporation | Albuquerque, NM 87109 | Oil & Gas Operator | Feb 1994 |
| 279 | Oiltech Inc | Yuba City, CA 95991 | Oil & Gas Operator | Dec 1984 |
| 280 | Oiltex, Inc. | Baltimore, MD 21221 | Oil & Gas Operator | Dec 2013 |
| 281 | Oilton Petroleum Inc | Oilton, OK 74052-0459 | Oil & Gas Operator | Oct 2001 |
| 282 | Oilton Resources, Inc. | Laredo, TX 78041 | Oil & Gas Operator | Jun 2025 |
| 283 | Oilwell Acquisition Co. | | Oil & Gas Operator | Jun 1999 |
| 284 | Oilwell Operator | | Gas Operator | Dec 1994 |
| 285 | Oilwell Operators, Inc. | Pampa, TX 79066 | Oil & Gas Operator | Jun 2025 |
| 286 | Oily Dog Operators Texas, LLC | Austin, TX 78746 | Oil Operator | Jun 2025 |
| 287 | Ojai Oil Company | Camarillo, CA 93012 | Oil & Gas Operator | Mar 2025 |
| 288 | Ojb, Inc. | Buda, TX 78610 | Oil & Gas Operator | Mar 2013 |
| 289 | Ojt, LLC | Richmond, TX 77469 | Oil Operator | Jun 2025 |
| 290 | Ok Arena Operating Company | Oklahoma City, OK 73101 | Oil & Gas Operator | Jun 2025 |
| 291 | Ok Oil Company, Inc. | Bivins, TX 75555 | Oil & Gas Operator | Feb 2013 |
| 292 | Ok Operating Co | Midland, TX 79702 | Oil & Gas Operator | Aug 1999 |
| 293 | Ok Production Services Inc | Broken Arrow, OK 74014 | Oil & Gas Operator | Feb 2025 |
| 294 | Ok-La-Tex Production, Inc. | | Oil & Gas Operator | Jan 1982 |
| 295 | Okc Energy Corporation | Oklahoma City, OK 73120-3119 | Oil & Gas Operator | Nov 2014 |
| 296 | Okemah Production Inc | | Oil Operator | Dec 2005 |
| 297 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Feb 2025 |
| 298 | Okie Oil Inc | Sapulpa, OK 74067-0290 | Oil & Gas Operator | Mar 2011 |
| 299 | Okie Operating Company, LTD. | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2025 |
| 300 | Okkatahula, Inc. | | Oil Operator | Nov 1978 |