| Wildnite AS | Information & communication | 2019 |
| Wilfred Invest AS | Financial services | 2005 |
| Willys AS | Real estate | 1968 |
| Windup AS | Professional & scientific | 2011 |
| Wingflex AS | Professional & scientific | 2025 |
| Winsnes Consulting AS | Information & communication | 2025 |
| Wongs AS | Real estate | 2016 |
| Woodside AS | Hospitality | 2026 |
| Woomultistore AS | Information & communication | 2020 |
| Wurk AS | Information & communication | 2000 |
| Wynn Soft AS | Information & communication | 2012 |
| Xeosol Norge AS | Information & communication | 2022 |
| Xtenso Event AS | Education | 2016 |
| Ymy Holding AS | | 2014 |
| Yourex Norge AS | Wholesale & retail | 2016 |
| Yva Holding AS | | 2025 |
| Zanerio Group AB Nuf | Information & communication | 2014 |
| Zarina AS | Wholesale & retail | 2001 |
| Zbar Travel Norway AS | Administrative & support | 2010 |
| Zbridge Limited | Information & communication | 2014 |
| Zeronorth Norway AS | Information & communication | 2022 |
| Zikzac Service AS | Construction | 2019 |
| ZLZ AS | Hospitality | 2018 |
| Zpire Limited Nuf | Professional & scientific | 2010 |
| Åkrene Mek Verksted AS | Manufacturing | 1982 |
| Åpen Barnehage Normisjon Lillestrøm AS | Education | 2020 |
| Ø Kildahl Invest AS | Real estate | 2009 |
| Ødegården Og Andersen AS | Construction | 1990 |
| Øie AS | Real estate | 2017 |
| Øie Gruppen AS | Professional & scientific | 1982 |
| Øie Sørum AS | Real estate | 1998 |
| Økonomiteam Skien AS | Professional & scientific | 2005 |
| Ølk Invest AS | | 2026 |
| Øsimonsen Holding AS | | 2026 |
| Østaveien Eiendom AS | Real estate | 2025 |
| Østbanernes Forbruksforening SA | Real estate | 1886 |
| Østheim Holding AS | Wholesale & retail | 2005 |
| Østheim Park Utvikling AS | Real estate | 2018 |
| Østlandske Boligstiftelser Ans | Real estate | 1991 |
| Østlandske Portservice AS | Wholesale & retail | 2025 |
| Øvre Grønlivei AS | Real estate | 2020 |
| Øvre Hallingdal Kraftproduksjon AS | Energy | 2004 |
| Øyelege Håkon Øritsland AS | Health & social care | 2014 |
| Øyvind Ruud Invest AS | | 2023 |
| Øyvind Wahl Invest AS | | 2021 |