| AS Linnes | Construction | 1986 |
| AS Ljan Terrasse | Households | 1952 |
| AS Lyngtun | Administrative & support | 1984 |
| AS Lysedahl Invest | Financial services | 1990 |
| AS Lysefjell | Financial services | 2005 |
| AS Lilleakerveien 23 | Manufacturing | 1956 |
| AS Løvenskioldsgate 11 | Households | 1933 |
| AS Løvenskioldsgt 3 | Households | 1910 |
| AS Magnus Bergs Gate NR 1 | Households | 1914 |
| AS Majorstuveien 11 | Households | 1962 |
| AS Majorstuveien 15 | Households | 1921 |
| AS Malerhaugens Byggeselskap | Households | 1923 |
| AS Mannen Bak Døra | Financial services | 2005 |
| AS Marcus Thranes Gate 7, 9 Og 11 (Tidligere Sandakerveien 11) | Households | 1935 |
| AS Maridalsveien 205 | Households | 1939 |
| AS Marienlystbygg Vii | Households | 1939 |
| AS Mascot Holding | Real estate | 1967 |
| AS Master Trading | Financial services | 1971 |
| AS Med-Lab | Health & social care | 1982 |
| AS Midtåsen 45 | Real estate | 1966 |
| AS Mogens Thorsensgate 1 | Households | 1928 |
| AS Mogens Thorsensgate 11 | Households | 1924 |
| AS Mogens Thorsensgt 1 B | Households | 1928 |
| AS Mogens Thorsensgt 5 | Households | 1926 |
| AS Monas | Financial services | 2005 |
| AS Mortenstunet | Households | 1955 |
| AS Mufasa | | 2020 |
| AS Munkedamsv 80 | Households | 1948 |
| AS Munkedamsveien 75 | Households | 1938 |
| AS Munkedamsveien 79 | Households | 1931 |
| AS Mølledrift | Real estate | 1991 |
| AS Nationen | Information & communication | 1918 |
| AS Neraal & Co | Manufacturing | 1957 |
| AS Nestlé Norge | Wholesale & retail | 1915 |
| AS Niels Juels Gate 7 | Households | 1915 |
| AS Ninolab | Wholesale & retail | 2017 |
| AS Nobelsgate 17 | Real estate | 1932 |
| AS Nobelsgate 20 | Households | 1929 |
| AS Nobelsgate 21 | Real estate | 1930 |
| AS Nobelsgate 23 | Households | 1929 |
| AS Nor Swiss | Wholesale & retail | 1973 |
| AS Nordengveien 61 | Real estate | 1994 |
| AS Nordic Fuel Supply | Wholesale & retail | 2019 |
| AS Nordstrandshøiden | Real estate | 1915 |
| AS Normark | Wholesale & retail | 2009 |
| AS Norse Crown Company Ltd | Wholesale & retail | 1930 |
| AS Norsk Labrador- & Granitindustri | Mining & quarrying | 1911 |
| AS Norske Telektron | Wholesale & retail | 1984 |
| AS Nortax | Real estate | 1990 |
| AS Nybygg | Households | 1915 |
| AS Nils Juelsgt 66 B | Real estate | 1961 |
| AS Nobelsgate 43 | Real estate | 1935 |
| AS Nordengveien 74 | Households | 1962 |
| AS Nördd+(Skyteknikk) | Information & communication | 2023 |
| AS Observatoriegaten 10 | Households | 1951 |
| AS Odden | Real estate | 1990 |
| AS Odinsgate 17 | Real estate | 1931 |
| AS Odinsgate 25 | Households | 1915 |
| AS Odinvest | Real estate | 1981 |
| AS Ole Vigsgate 14 | Real estate | 1938 |
| AS Olsen & Ugelstad | | 1972 |
| AS Orthas | Health & social care | 2022 |
| AS Oscars Gate 69 | Households | 1917 |
| AS Oscarsgate 43 | Households | 1916 |
| AS Oscarsgate 8 C | Real estate | 1949 |
| AS Oscarsgt 13 | Households | 1915 |
| AS Oscarsgt 7 a | Households | 1933 |
| AS Oscarsgt 7 B | Households | 1932 |
| AS Oslo Bremseservice | Other services | 1970 |
| AS Oslo Sporveier | Transport & logistics | 2008 |
| AS Palace Grill | Hospitality | 1987 |
| AS Parkgaarden Holding | Real estate | 2019 |
| AS Parks | Arts & recreation | 2011 |
| AS Parks Holding | Arts & recreation | 2020 |
| AS Parkteateret | Real estate | 1918 |
| AS Parkveien 62 | Real estate | 1914 |
| AS Partrade | Wholesale & retail | 1970 |
| AS Penta Bird Ventures | | 2018 |
| AS Petter W Eckhoff | Professional & scientific | 1973 |
| AS Pihlløkken Byggeselskap | Households | 1934 |
| AS Pihlsg 2 | Households | 1936 |
| AS Pit | Other services | 1990 |
| AS Prinsens Gate 1 | Real estate | 1923 |
| AS Prinsensgate 6 | Real estate | 1932 |
| AS Privat Finance | Professional & scientific | 1972 |
| AS Produktledelse | Information & communication | 2024 |
| AS Professor Dahlsgate 16 | Households | 1916 |
| AS Protect | | 1984 |
| AS Quatro | Professional & scientific | 1938 |
| AS Rassie | Real estate | 1989 |
| AS Real-Forvaltning | Professional & scientific | 1987 |
| AS Realbygg | Construction | 1989 |
| AS Reverti | Real estate | 2015 |
| AS Riiser & Co | | 2025 |
| AS Ringgaten Byggeselskap III | Households | 1934 |
| AS Rita Korsettsalong | Wholesale & retail | 1936 |
| AS Ronile | Financial services | 1992 |
| AS Rosenkrantzg 13 | Real estate | 1988 |
| AS Rosenlundgaten 6 | Households | 1932 |
| AS Rundsaga Bruk | Manufacturing | 1955 |