| Name of the place | CERL ID of a place | Country | Longitude | Latitude | |
|---|---|---|---|---|---|
| Opava | cnl00012517 | Czech Republic | 17.8991666666667 | 49.9330555555556 | |
| Oppenheim | cnl00012525 | Germany | 8.35972222222222 | 49.85 | |
| Oran | cnl00018393 | Algeria | — | — | |
| Orange | cnl00012528 | France | 4.79944444444444 | 44.13 | |
| Orbe | cnl00021253 | Switzerland | — | — | |
| Orbessan | cnl00024123 | France | 0.6103 | 43.5447 | |
| Orgelet | cnl00018852 | France | 5.6111 | 46.5231 | |
| Orléans | cnl00016168 | France | 1.89916666666667 | 47.92 | |
| Orléans [non-CERL] | — | — | — | — | |
| Ornans | cnl00026913 | France | 6.15 | 47.1 | |
| Orsoy | cnl00034691 | Germany | — | — | |
| Orthez | cnl00002616 | France | -0.766666666666667 | 43.4830555555556 | |
| Orton | cnl00017297 | England | — | — | |
| Orzinuovi | cnl00018388 | Italy | 9.925 | 45.403333 | |
| Oschatz | cnl00012558 | — | 13.1194444444444 | 51.2994444444444 | |
| Osimo | cnl00012562 | Italy | 13.48 | 43.4791666666667 | |
| Osnabrück | cnl00012513 | Germany | 8.05 | 52.27 | |
| Ostel | cnl00022883 | France | — | — | |
| Ostende | cnl00012570 | Belgium | 2.92 | 51.22 | |
| Osterode | cnl00012468 | — | 10.1794444444444 | 51.7194444444444 | |
| Ostiglia | cnl00003529 | Italy | 11.1333333333333 | 45.7833333333333 | |
| Otranto | cnl00003530 | Italy | 18.4833333333333 | 40.15 | |
| Ottery Saint Mary (Devon) | cnl00032276 | England | -3.279 | 50.752 | |
| Ouarville | cnl00019601 | — | — | — | |
| Oud-Alblas | — | Netherlands | 4.704722 | 51.856944 |