ABSTRACT Writers on Norwegian economic history often claim that industries related to the sea played a major role in the Norwegian economy for centuries. However, little has been done to quantify this sector’s contribution to the economy. The present paper seeks to quantify the size of the key offshore industries compared to GDP and exports. To do so it has been necessary to draw on new historical national account calculations and export data in addition to compute new series Based on these calculations we find that the offshore sector made up a significant part of Norwegian GDP, and a dominant part of exports, 1816–2021. As a share of the total economy the sector’s traditional industries, i.e. fishing ari and ocean transport were in sum stable until the late 1950s in the long-run. Thereafter they shrunk rapidly, when the takeoff of the new offshore industry, oil and gas extraction from the continental shelf from the 1970s, made the offshore economy reach new heights in the decades to follow. This paper quantifies this development.