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| NYTTBYGG AS | 913359771 | SARPSBORG |
| NYTT PROSJEKT AS | 974389657 | OSLO |
| NYVOLD INSTALLASJON AS | 957724787 | OPPDAL |
| NYVOLL CONSULT AS | 993172537 | NITTEDAL |
| NZ RØRSERVICE AS | 922129800 | LILLESTRØM |
| Ø.ANTONSEN AS | 964377111 | BERGEN |
| O A SANNE AS | 932521806 | MOLDE |
| OBAS ENTREPRENØR AS | 960018095 | BERGEN |
| OBB AS | 921230125 | BJØRNAFJORDEN |
| OB BRENDEMOEN AS | 965678492 | NORD-FRON |
| ØBE AS | 921863993 | ULLENSAKER |
| OBERRAUTER BYGG OG SPRENGNING AS | 915540813 | VESTBY |
| OBOS BLOCK WATNE ENTREPRENØR AS | 930061212 | OSLO |
| OBOS PROSJEKT AS | 931536532 | OSLO |
| OBRON GRUPPEN AS | 998300665 | TRONDHEIM |
| ØB RØR AS | 936606040 | ØRSTA |
| ØB-TAK AS | 971072830 | OSLO |
| OCAB AS | 916326211 | BÆRUM |
| ODAL ANLEGGSDRIFT AS | 932475057 | NORD-ODAL |
| ODAL BYGG AS | 931933795 | SØR-ODAL |
| ODAL ENTREPRENØR AS | 994449826 | SØR-ODAL |
| O D BYGG AS | 924661399 | HØYANGER |
| ODD ARNE AARSTAD | 977105579 | KONGSVINGER |
| ODD BARTHO-HANSEN & SØNNER AS | 955499697 | FÆRDER |
| ODD BJERKEVOLL AS | 942654723 | VESTNES |
| ODD EINAR KNE AS | 974904535 | STEINKJER |
| ODD ERLING LØVØY | 968174835 | HERØY (MØRE OG ROMSDAL) |
| ODD FARMEN AS | 925415693 | LARVIK |
| ODD HAGERUD AS | 976018192 | EIDSKOG |
| ODD HEIBERG AS | 984556128 | HORTEN |
| ODD MATHISEN AS | 979924410 | ALTA |
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| ODD STENSVOLD AS | 995680084 | LARVIK |
| ODDVAR MELING AS | 980151794 | STAVANGER |
| ODDVAR ØYGARD AS | 985793581 | ÅL |
| ØDEGAARD ANLEGG AS | 992170905 | BRØNNØY |
| ØDEGAARD OG STERTEN AS | 997907116 | BÆRUM |
| ØDEGÅRD BYGG OG MASKIN AS | 919232773 | LUSTER |
| ØDEGÅRDENS PLANTESKOLE OG UTEMILJØ AS | 983136613 | GRIMSTAD |
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| ØEN HYTTEBYGG AS | 892353662 | HOL |
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| OFFJORD-ENTREPRENØR AS | 932172798 | OSLO |
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| OHNSTAD AS | 923363270 | LARVIK |
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| O J MILJETEIG AS | 938173605 | HAUGESUND |
| 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 |
| OKKENHAUG ENTREPRENØR AS | 911851482 | LEVANGER |
| O K LIE AS | 982049741 | ØVRE EIKER |
| Ø.K MASKINDRIFT AS | 918697365 | ØSTRE TOTEN |
| ØKO AS | 924824484 | KRISTIANSAND |
| ØKO GRØNT AS | 979908431 | VINJE |
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| O. KRISTENSEN BYGG AS | 915330940 | SANDNES |
| O. KRISTIANSEN ENTREPRENØR AS | 925263052 | ÅSNES |
| OKSNES ANLEGG & MASKIN AS | 998533880 | ASKØY |
| ØKSNES ENTREPRENØR AS | 976754301 | ØKSNES |
| 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 |
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| OLAF PETTERSEN AS | 980383644 | HERØY (N.) |
| O LANGSETER & SØNN AS | 926744518 | NORDRE FOLLO |
| OLA RAAEN AS | 948698293 | STJØRDAL |
| 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 |