 | OLIMB RØRFORNYING AS | 997447018 | RÅDE |
| OLIVA PARK AS | 920721095 | SARPSBORG |
| O L KYTHE AS | 935252601 | VOSS |
| O.Løkken A/S | 931515829 | TRONDHEIM |
| OLS1 HOLDING AS | 920471129 | LINDESNES |
| OLS1VVS AS | 820951522 | DRAMMEN |
| OLSENBYGG GRIMSTAD AS | 998339898 | GRIMSTAD |
| OLSEN MASKINENTREPRENØR AS | 915939686 | BJØRNAFJORDEN |
| OLSEN MASKIN & TRANSPORT AS | 919898690 | DØNNA |
| OLSEN RØRLEGGERSERVICE AS | 927532751 | STANGE |
| OLSET KSU AS | 821996112 | KRISTIANSUND |
| OL TO VVS AS | 983232108 | VENNESLA |
| OLYMPUS VVS AS | 823874642 | OSLO |
| OMA MASKIN | 861758532 | TIME |
| OM BAKKEN BYGG AS | 966707496 | NORD-FRON |
| O&M BYGG AS | 922083134 | BERGEN |
| OMC BYGG AS | 998360617 | BERGEN |
| OMDAL BETONG AS | 912772381 | LILLESAND |
| OMEGA 365 AREAL AS | 986930264 | VINDAFJORD |
| OMEGA AKERHOLDT AS | 913130529 | ASKER |
| OMEGA TDS AS | 991091270 | TØNSBERG |
| OMEGA VVS BERGER | 922809488 | ASKER |
| ØMF ASKER RINGERIKE AS | 830220852 | ASKER |
| ØMF EVENSEN & EVENSEN AS | 984958552 | LILLEHAMMER |
| ØMF HAMAR AS | 930220760 | HAMAR |
| ØMF ØSTFOLD AS | 930220841 | MOSS |
| ØMF ROMERIKE KONGSVINGER AS | 911669668 | KONGSVINGER |
| ØMF WITO AS | 884587832 | EIDSKOG |
| OMKRI PLAN & ARKITEKTUR AS | 932155931 | TØNSBERG |
| OMLAND MASKIN AS | 990808333 | KVINESDAL |
| OMLID AS | 928821595 | EIGERSUND |
| OMMEDAL & SØNNER AS | 934033302 | TØNSBERG |
| OM MILJØTEKNIKK AS | 923380701 | BERGEN |
| OM SIMONSEN MASKIN AS | 999568033 | MÅLSELV |
| OMT BBL | 948054353 | NARVIK |
| O. MYDLAND MASKIN AS | 984454945 | SOKNDAL |
| ONARHEIM AS | 946471623 | OSLO |
| ON ARKITEKTER OG INGENIØRER AS | 992619295 | ORKLAND |
| ONECO ELEKTRO AS | 996669173 | OSLO |
| ONECO MOBIL AS | 925894168 | OSLO |
| ONECO NETWORKS AS | 987210001 | OSLO |
| Ø. NORDBERG BYGGPROSJEKTERING | 889468742 | SARPSBORG |
| O NØRSTEBØ & SØNN AS | 977046572 | NORE OG UVDAL |
| ONOS OLE NORDMO & SØNN AS | 950674237 | MÅLSELV |
| ONØY MASKINSTASJON AS | 923112065 | LURØY |
| ONSØIEN MASKIN AS | 996785475 | SKAUN |
| ONSØY RØR AS | 924329009 | FREDRIKSTAD |
| ONSØY RØRLEGGERBEDRIFT AS | 936722288 | FREDRIKSTAD |
| OPAK AS | 960816862 | OSLO |
| OP BYGG AS | 927472236 | OSLO |