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| Oak Ridge Capital AS | Tønsberg | 2020 |
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| Offshore & Trawl Supply AS | Valderøya | 1990 |
| Offshore Equipment Chartering | Be-2910 Essen | 2016 |
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| Ogna Sider Og Skoghage AS | Sandnes | 2023 |
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| Ogna Sveis Holding AS | Vigrestad | 1994 |
| Ogtech AS | Bjorbekk | 2019 |
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| Ohmart/Vega Corporation | Oslo | 2008 |