 | OFOTEN MEK AS | 924426993 | NARVIK |
| OFOTEN RØR AS | 968277898 | NARVIK |
| O.HANSEN & SØNNER AS | 934235347 | KARMØY |
| Ø. HELLESØY RØRLEGGER SERVICE | 990118469 | BERGEN |
| OHNSTAD AS | 923363270 | LARVIK |
| ØIJORD & AANES ENTREPRENØRFORRETNING AS | 957749933 | RANA |
| ØISETH MONTASJE AS | 935096839 | KONGSVINGER |
| ØISTAD ELEKTRO AS | 988277231 | GRAN |
| ØISTEIN ASK ANDERSEN | 970335633 | SANDEFJORD |
| ØIVIND ÅSMANN | 968352113 | ULLENSAKER |
| ØIVIND BRÅTHEN AS | 966890967 | ØVRE EIKER |
| ØIVIND FJELD BYGG OG TØMRERMESTER AS | 982205492 | BÆRUM |
| ØIVIND LYSTAD AS | 936860478 | KRISTIANSUND |
| O J MILJETEIG AS | 938173605 | HAUGESUND |
| O.J. RØR AS | 998554675 | BÆRUM |
| ØJ RØR AS | 914179165 | KRØDSHERAD |
| OK ANLEGG AS | 912697290 | VÅLER (ØSTFOLD) |
| OK ANLEGGSSERVICE AS | 984797540 | DRAMMEN |
| OK BAD AS | 992779926 | TIME |
| OK BYGG & ANLEGG AS | 928202720 | OVERHALLA |
| OK+ BYGG AS | 933108279 | BERGEN |
| ØK-BYGG AS | 924531215 | GRAN |
| OK ENTREPRENØR AS | 995789418 | ÅLESUND |
| OKER ARKITEKTUR AS | 976186419 | OSLO |
| O K LIE AS | 982049741 | ØVRE EIKER |
| Ø.K MASKINDRIFT AS | 918697365 | ØSTRE TOTEN |
| ØKO AS | 924824484 | KRISTIANSAND |
| ØKO GRØNT AS | 979908431 | VINJE |
| ØKOHJEM ENTREPRENØR AS | 924527528 | ØVRE EIKER |
| ØKONOMIBYGG ARKITEKTUR AS | 985223769 | OSLO |
| ØKOVENT AS | 912592715 | TRONDHEIM |
| O. KRISTENSEN BYGG AS | 915330940 | SANDNES |
| O. KRISTIANSEN ENTREPRENØR AS | 925263052 | ÅSNES |
| OKSNES ANLEGG & MASKIN AS | 998533880 | ASKØY |
| ØKSNES ENTREPRENØR AS | 976754301 | ØKSNES |
| OKS-TJENESTER AS | 918598103 | STJØRDAL |
| OK TRANSPORT & MASKIN AS | 813874792 | TYSNES |
| O.K. TVEIT AS | 998557712 | KARMØY |
| OK VARMETEKNIKK AS | 994277626 | ØVRE EIKER |
| OK VEDLIKEHOLD AS | 988210595 | AVERØY |
| OK VENTILASJON AS | 968407147 | ÅL |
| OLAF B TERJESEN AS | 936016081 | FÆRDER |
| Olaf E Eriksen AS Entreprenørforretning | 911492377 | OSLO |
| OLA FISKETJØN AS | 966024607 | SULDAL |
| OLAF JOHANSENS EFTF AS | 944685987 | OSLO |
| OLAF O. RUKKE AS | 945665076 | NESBYEN |
| OLAF PETTERSEN AS | 980383644 | HERØY (N.) |
| O LANGSETER & SØNN AS | 926744518 | NORDRE FOLLO |
| OLA RAAEN AS | 948698293 | STJØRDAL |
| OLAV AGER-WICK AS | 929345223 | ARENDAL |