 | 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 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 |
| 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 |
| OLAF JOHANSENS EFTF AS | 944685987 | OSLO |
| OLAF O. RUKKE AS | 945665076 | NESBYEN |
| OLAF PETTERSEN AS | 980383644 | HERØY (N.) |
| OLA HOFF ENTREPRENØR AS | 982010004 | GRAN |
| O LANGSETER & SØNN AS | 926744518 | NORDRE FOLLO |
| OLA RAAEN AS | 948698293 | STJØRDAL |
| OLAUSSEN RÅDGIVENDE INGENIØRKONTOR AS | 970931783 | TØNSBERG |
| OLAV AGER-WICK AS | 929345223 | ARENDAL |
| OLAV A. VÅGE MASKIN AS | 916941161 | SANDE (MØRE OG ROMSDAL) |
| OLAV ERIK HAGEN AS | 966265949 | STRYN |
| OLAV H HAUSO | 970203532 | ULLENSVANG |
| OLAV HJELMESET AS | 982063337 | GLOPPEN |
| OLAV HOVDE AS | 887832552 | RINGSAKER |
| OLAV KRISTIAN OPPEDAL | 970357947 | LARVIK |
| OLAV LANGLO | 979429967 | TRONDHEIM |
| OLAV O. HÆREID AS | 948839946 | ÅRDAL |
| OLAV SKARET | 983401686 | GOL |
| OLAV SOLBERG AS | 941579833 | OPPDAL |
| OLAV SOLVANG AS | 976502337 | TOKKE |
| OLAV STEINAR BJORDAM | 970895434 | BAMBLE |
| OLDEN RØR AS | 939792686 | STRYN |