| Prefix | County | County code |
| OM1 | Bratislava I | BAA |
| Bratislava II | BAB | |
| Bratislava III | BAC | |
| Bratislava IV | BAD | |
| Bratislava V | BAE | |
| Malacky | MAL | |
| Pezinok | PEZ | |
| Senec | SEN | |
| OM2 | Trnava | TRN |
| Dunajská Streda | DST | |
| Galanta | GAL | |
| Hlohovec | HLO | |
| Piešťany | PIE | |
| Senica | SEA | |
| Skalica | SKA | |
| OM3 | old calls from Czechoslovakia, prefix moved from OK3 => OM3 | |
| OM4 | Trenčín | TNC |
| Bánovce nad Bebravou | BAN | |
| Ilava | ILA | |
| Myjava | MYJ | |
| Nové mesto nad Váhom | NMV | |
| Partizánske | PAR | |
| Považská Bystrica | PBY | |
| Prievidza | PRI | |
| Púchov | PUC | |
| OM5 | Komárno | KOM |
| Levice | LVC | |
| Nitra | NIT | |
| Nové Zámky | NZA | |
| Topoľčany | TOP | |
| Šaľa | SAL | |
| Zlaté Moravce | ZMO | |
| OM6 | Čadca | CAD |
| Dolný Kubín | DKU | |
| Liptovský Mikuláš | LMI | |
| Martin | MAR | |
| Žilina | ZIL | |
| Bytča | BYT | |
| Kysucké Nové Mesto | KNM | |
| Námestovo | NAM | |
| Ružomberok | RUZ | |
| Turčianske Teplice | TTE | |
| Tvrdošín | TVR | |
| OM7 | Banská Bystrica | BBY |
| Banská Štiavnica | BST | |
| Brezno | BRE | |
| Detva | DET | |
| Krupina | KRU | |
| Lučenec | LUC | |
| Poltár | POL | |
| Revúca | REV | |
| Rimavská Sobota | RSO | |
| Zvolen | ZVO | |
| Žiar nad Hronom | ZIH | |
| Veľký Krtíš | VKR | |
| Žarnovica | ZAR | |
| OM8 | ||
| Košice I | KEA | |
| Košice II | KEB | |
| Košice III | KEC | |
| Košice IV | KED | |
| Košice okolie | KEO | |
| Gelnica | GEL | |
| Michalovce | MIC | |
| Rožňava | ROZ | |
| Sobrance | SOB | |
| Spišská Nová Ves | SNV | |
| Trebišov | TRE | |
| OM9 | special stations (upon special permission) | |
| OM0 | Prešov | PRE |
| Bardejov | BAR | |
| Humenné | HUM | |
| Kežmarok | KEZ | |
| Levoča | LEV | |
| Medzilaborce | MED | |
| Poprad | POP | |
| Sabinov | SAB | |
| Snina | SNI | |
| Stará Ľubovňa | SLU | |
| Stropkov | STR | |
| Svidník | SVI | |
| Vranov nad Topľou | VRT | |