| Abbreviation |
Organisation |
| OAA |
Orient Airlines Association, Manila |
| OAEC |
Organization for Asian Economic Co-operation |
| OAS |
Organization of American States, Washington |
| OAU |
Organization of African Unity,
Addis Ababa |
| OCAS |
Organization of Central American States,
San Salvador |
| OCTI |
Office Central des Transports Internationaux
par Chemins de Fer, (Central Office for International Railway Transport),
Berne |
| OECD |
Organization for Economic Co-operation
and Development (Organisation de Co-operation et de Developpement
Economiques, OCDE), Paris |
| OPEC |
Organization of Petroleum Exporting Countries,
Vienna |
| OSShD |
Organization for the Collaboration of Railways,
Warsaw |
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