List of reporting marks: O

O

 * OACX - Central Transportation, Inc.
 * OAR - Old Augusta Railroad
 * OCCU - ATS Container Leasing SA
 * OCCX - Occidental Chemical Company
 * OCE - Oregon, California and Eastern Railway
 * OCEU - Oceanex Inc.
 * OCFX - Owens Corning Fiberglass
 * OCLU - Overseas Containers, Ltd.
 * OCNU - Ocean Lines, Inc.
 * OCPX - Occidental Chemical Company; Oxy Vinyls
 * OCR - Oklahoma Central Railroad
 * OCRR - Ottawa Central Railway
 * OCRX - Oil Creek Refining Company
 * OCSU - Scripps Institute of Oceanography
 * OCTL - Oil Creek and Titusville Lines
 * OCTR - Octoraro Railway
 * OCTX - Octel America, Inc.
 * ODTX - Oil-Dri Corporation of America
 * OEDX - Ohio Edison Company
 * OERX - Southern California Railway Museum
 * OFCX - Ortner Freight Car Company
 * OFOX - Residco
 * OFSX - Tucson Electric Power Company
 * OGEE - Ogeechee Railway
 * OGEX - Oklahoma Gas and Electric Company
 * OGSX - Iowa Southern Utilities Company
 * OHCR - Ohio Central Railroad
 * OHFX - Fluor Daniel Fernald
 * OHIC - Ohi-Rail Corporation
 * OHIO - Ohio Terminal Railway
 * OHKU - Ohka American, Inc.
 * OHOX - United States Department of Energy (Ohio Field)
 * OHPA - Ohio and Pennsylvania Railroad
 * OHRY - Owego and Harford Railway
 * OILX - GE Rail Services
 * OJGX - Oscar J. Glover
 * OJTX - Tauber Transportation Company
 * OKAN - Okanagan Valley Railway (OmniTRAX)
 * OKCE - Okarche Central Railway
 * OKCX - Lone Star Industries
 * OKKT - Oklahoma, Kansas and Texas Railroad; Union Pacific Railroad
 * OLAU - Occidental Chemical Corporation
 * OLB - Omaha, Lincoln and Beatrice Railway
 * OLDX - Old Line Holding Company, Inc.
 * OLGX - Ineos Oligomers USA, LLC
 * OLLU - Ocean Leasing, Ltd.
 * OLNX - Olin Corporation
 * OLO - Ontario L'Orignal Railway
 * OLYR - Olympic Railroad
 * OLYU - Olympic Container Corporation
 * OLYR - Olympic Railroad
 * OLYX - Olympia Petroleum, Inc.
 * OLYZ - Showa Line, Ltd.
 * OMAX - Omaha Public Power District
 * OMID - Ontario Midland Railroad
 * OMLP - Ohio Midland Light and Power
 * OMLX - OmniTRAX Leasing, Ltd.
 * OMNX - Omnisource; Steel Dynamics.
 * OMRX - Ozark Mountain Railcar
 * OMSX - Ohio Mulch; J. T. Leasing, Inc.
 * ONCT - Ontario Central Railroad
 * ONER - Ontario Eastern Railroad
 * ONSX - Oglebay Norton Industrial Sands, Inc.
 * ONT - Ontario Northland Railway
 * ONTA - Ontario Northland Railway
 * ONTX - On-Track Railcar Services, Inc.
 * ONW - Oregon and Northwestern Railroad
 * ONYX - American Colloid Company
 * OOCZ - Orient Overseas Line, Inc.
 * OOLU - OOCL
 * OOOX - Osborne, Inc.
 * OOUU - Orient Overseas Line, Inc.
 * OPE - Oregon, Pacific and Eastern Railway
 * OPIX - Equistar Chemicals
 * OPPX - Omaha Public Power District
 * OPR - Oregon Pacific Railroad
 * OPSU - EMP
 * OPSX - Public Service Company of Oklahoma
 * OPT - Orange Port Terminal Railway
 * OPX - Ohio Power Company
 * OR  - Owasco River Railway
 * ORA - Ormet Railroad
 * ORCU - BSL Transport
 * OREX - Oregon Department of Agriculture
 * OROX - United States Department of Energy (Oak Ridge Operations Office)
 * ORR - Osage Railroad
 * OSCZ - Intermodal Services, Inc.
 * OSL - Oregon Short Line; Union Pacific Railroad
 * OSRX - Ontario Southland Railway
 * OSSU - Eurovos B.V.
 * OTCO - Owensville Terminal Company
 * OTCR - Oakdale Traction Corporation
 * OTDX - Greenbrier Leasing Corporation
 * OTPX - Otter Tail Power Company
 * OTR - Oakland Terminal Railway
 * OTRX - On-Track Railway Services, Ltd.
 * OTSX - On-Track Railway Services, Ltd.
 * OTT - Ottumwa Terminal Railroad
 * OTTX - TTX Corporation
 * OTVR - Otter Tail Valley Railroad (RailAmerica)
 * OUCH - Ouachita Railroad
 * OUCX - Orlando Utilities Commission
 * OURD - Ogden Union Railway and Depot Company
 * OVEX - Ohio Valley Electric Company
 * OVNZ - Overnite Transportation Company
 * OVO - Ottawa Valley Railway
 * OVR - Ohio Valley Railroad
 * OWIX - Old World Transportation, Ltd.
 * OWLU - Ocean World Lines, Inc.
 * OWSX - Oil Well Supply Company
 * OWTX - Shamrock Coal Company
 * OXYU - Eurotainer US, Inc.