| 1801 | OLDX | Old Line Holding Co., Inc. | added 1/92; 1/94-7/2000 | | NRHS |
| 1802 | OLDX | OLD LINE HOLDING COMPANY, INC | | | PWRC |
| 1803 | OLDX | Old Line Holding | | | RSRV |
| 1804 | OLE | Operadora de Lineas Ejecutivas S.A. de C.V. | Callsign: Operadora, | MEX | AVCODES |
| 1805 | OLE | Operadora de Lineas Ejecutivas | | | ICAO1 |
| 1806 | OLEA | OLEARY TRANSPORTATION CO, INC | | | SCAC3 |
| 1807 | OLEA | OUTLAW EAGLE MANUFACTURING LTD | | | SCAC4 |
| 1808 | OLEE | OLD LVIV EXPRESS | | | SCAC4 |
| 1809 | OLEO | OLERON TANKER S A | | | SCAC3 |
| 1810 | OLEP | OLYMPIC EXPRESS | | | SCAC3 |
| 1811 | OLEP | OFF LOAD EXPRESS | | | SCAC4 |
| 1812 | OLEQ | OVERLAND EQUINE EXPRESS | | | SCAC3 |
| 1813 | OLER | OLE ROCKNE | | | SCAC3 |
| 1814 | OLES | OLE SAN MIGUEL | | | SCAC4 |
| 1815 | OLFC | OLOFSSON CORP | | | SCAC3 |
| 1816 | OLFE | OLD FORT EXPRESS COMPANBY INC | | | SCAC3 |
| 1817 | OLFR | OZ-LU FURNITURE & DECOR | | | SCAC4 |
| 1818 | OLFU | OLVI FORWARDING LTD | | CY | BIC |
| 1819 | OLFV | ONLINE FREIGHT SERVICES INC | | | SCAC4 |
| 1820 | OLFW | OLYMPIC FREIGHTWAYS INC | | | SCAC3 |
| 1821 | OLFZ | OLYMPIC FOUNDRY | | | PWRC |
| 1822 | OLGI | OCEANICA LOGISTICS GROUP INC | | | SCAC4 |
| 1823 | OLGL | ORCHARDS LOGISTICS LLC | | | SCAC4 |
| 1824 | OLGT | OLINGER TRUCKING INC | | | SCAC3 |
| 1825 | OLGV | OCEAN LONGEVITY COMPANY | | | SCAC3 |
| 1826 | OLGV | OCEAN LONGEVITY CO LTD | | | SCAC4 |
| 1827 | OLGX | INOS Oligomers | added 1/2008 | | NAKINA |
| 1828 | OLGX | INEOS OLIGOMERS, DIV. INEOS USE LLC | | | PWRC |
| 1829 | OLGX | INEOS OLIGOMERS A DIVISION OF | | | SCAC4 |
| 1830 | OLHC | OLEAN HAULING CORP | | | SCAC3 |
| 1831 | OLHD | OLSON, HAROLD D | | | SCAC3 |
| 1832 | OLHI | OAK LODGE HOLDINGS INC | | | SCAC4 |
| 1833 | OLHK | OLD HICKORY TRANSPORTATION | | | SCAC3 |
| 1834 | OLHX | O.L. Hoese Co. (Merchants Despatch, Inc.) | 7/1935 | | NAKINA |
| 1835 | OLI | Ogden, Logan & Idaho Ry. Co. (Utah Idaho Central R.R. Co.) | 7/1923 | | NAKINA |
| 1836 | OLI | UTAH IDAHO CENTRAL RAILROAD CO. [OGDEN, LOGAN & IDAHO RWY. CO.] | | | PWRC |
| 1837 | OLIB | OFF LOGISTICS INC | | | SCAC4 |
| 1838 | OLIC | OLSON INTERMODAL COMPANY | | | SCAC3 |
| 1839 | OLIC | Olichon S.A.S. | | F | TRAFFIC |
| 1840 | OLIF | OFFICE LINE | | | SCAC4 |
| 1841 | OLIN | ONLINE TRANSPORT INC | | | SCAC4 |
| 1842 | OLIV | OLIVER FUELS & OILS INC | | | SCAC4 |
| 1843 | OLJQ | OLSON, JOHN A TRUCK LINE | | | SCAC3 |
| 1844 | OLJR | OLSON, JOHN ROY | | | SCAC3 |
| 1845 | OLJR | OLLERICH, JERALD | | | SCAC4 |
| 1846 | OLJT | OLDNER, JOHN TRUCKING COMPANY | | | SCAC3 |
| 1847 | OLKL | ORANGELINE TRUCKING LIMITED | | | SCAC4 |
| 1848 | OLKOL | ZNTK OLEŚNICA S.A. | | PL | VKM |
| 1849 | OLKT | OLIVER, W TRUCKING | | | SCAC3 |
| 1850 | OLL | Operadora Llaminmex, S.A. de C.V. | Callsign: Minmex, | MEX | AVCODES |
| 1851 | OLLC | OSPREY LINE LLC | | | SCAC4 |
| 1852 | OLLE | OLLIE MOVING & STORAGE | | | SCAC3 |
| 1853 | OLLI | ON LINE LOGISTICS INC | | | SCAC4 |
| 1854 | OLLS | ORAYON LOGISTICS LLC | | | SCAC4 |
| 1855 | OLLT | OTR LOGISTICS LLC | | | SCAC4 |
| 1856 | OLLU | OCEAN LEASING LTD. | | | PWRC |
| 1857 | OLLU | Ocean Leasing | | | RSRV |
| 1858 | OLMC | OCEAN LINK MARITIME S A | | | SCAC4 |
| 1859 | OLMF | OLYMPIC FREIGHTWAYS | | | SCAC3 |
| 1860 | OLMF | OLMEDO, FRANCISCO JAVIER | | | SCAC4 |
| 1861 | OLMG | OLYMPIAN MOVING & STORAGE INC | | | SCAC3 |
| 1862 | OLMJ | OLMSTEAD, JIM TRUCKING | | | SCAC3 |
| 1863 | OLMO | OIL MOP LLC | | | SCAC4 |
| 1864 | OLMP | OLYMPIA TRANSPORT INC | | | SCAC3 |
| 1865 | OLMP | OLYMPIA TRANSPORT INC | | | SCAC4 |
| 1866 | OLMS | OLMSTEAD FREIGHT LINES | | | SCAC3 |
| 1867 | OLMS | OLE MEXICAN FOODS INC | | | SCAC4 |
| 1868 | OLMT | OLMSTEAD & SONS | | | SCAC3 |
| 1869 | OLMU | OCEANUS LINE | | USA | BIC |
| 1870 | OLMV | OLSONS MOVING & STORAGE | | | SCAC3 |
| 1871 | OLND | OLAND TRUCK LINE | | | SCAC3 |
| 1872 | OLND | OSTLUND SUPPLY | | | SCAC4 |
| 1873 | OLNG | OLINGER TRANS INC | | | SCAC4 |
| 1874 | OLNK | OLSON TRUCKING | | | SCAC3 |
| 1875 | OLNL | OLNEY, LAURENCE ENTR | | | SCAC3 |
| 1876 | OLNL | OL N LO EXPRESS INC | | | SCAC4 |
| 1877 | OLNP | OLSON, PAUL E TRUCKING | | | SCAC3 |
| 1878 | OLNP | OVERSEAS LNG H2 CORPORATION | | | SCAC4 |
| 1879 | OLNQ | OLSEN, O F MOVING & STORAGE | | | SCAC3 |
| 1880 | OLNS | OLDENBERG & SON INC | | | SCAC3 |
| 1881 | OLNT | OLSEN, S G TRUCKING | | | SCAC3 |
| 1882 | OLNT | OLNEY TRANSPORTATION INC | | | SCAC4 |
| 1883 | OLNV | OLNEY VAN & STORAGE INC | | | SCAC3 |
| 1884 | OLNX | Olin Corp. | added 10/1977; 1/1980-7/2005 | | NAKINA |
| 1885 | OLNX | Olin Corp. | 1/80-7/2000 | | NRHS |
| 1886 | OLNX | OLIN CORPORATION | | | PWRC |
| 1887 | OLNX | Olin Corporation | | | RSRV |
| 1888 | OLNX | OLIN CORPORATION | | | SCAC4 |
| 1889 | OLNY | OLNEY TRUCKING | | | SCAC3 |
| 1890 | OLO | Soloflight | Callsign: Solo, | GB | AVCODES |
| 1891 | OLO | Soloflight | | | ICAO1 |
| 1892 | OLO | Ontario L'Orignal Ry., Inc. | 7/2000-7/2005 | | NAKINA |
| 1893 | OLO | Ontario L'Orignal Ry., Inc. | Jul-00 | | NRHS |
| 1894 | OLO | ONTARIO L'ORIGNAL RAILWAY INC. | | | PWRC |
| 1895 | OLO | Ontario L'Orignal Railway | | | RSRV |
| 1896 | OLO | ONTARIO L'ORIGNAL RAILWAY INC | | | SCAC4 |
| 1897 | OLOB | ORT LOGISTICS | | | SCAC4 |
| 1898 | OLOF | ONESOURCE LOGISTICS | | | SCAC4 |
| 1899 | OLOM | Dopravni podnik mesta Olomouce | Real: DPMO, City: Olomouc | CZ | TRAFFIC |
| 1900 | OLOS | OAKLAND LOGISTICS SERVICE INC | | | SCAC4 |
