Olsen worked in the family firm, Fred. Olsen & Co. dating from 1914. Together with his brother Thomas Fredrik Olsen, he was a partner from 1922. After their father's death in 1933, the brothers took over as leaders of the company. From 1933 he was CEO of the firm. During his leadership, the company expanded, entering the aviation business with its own airline Fred. Olsen Flyselskap. In addition it obtained partial ownership interests in Scandinavian Airlines System, Widerøe's Flyveselskap AS and Sterling Airlines A/S.
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