The North Sea turned out to present many technical challenges for production and exploration, and Norwegian companies invested in building capabilities to meet these challenges. A number of engineering and construction companies emerged from the remnants of the largely lost shipbuilding industry, creating centers of competence in Stavanger and the western suburbs of Oslo. Stavanger also became the land-based staging area for the offshore drilling industry. Due to refinery needs when making special qualities of commercial oils, Norway imported NOK 3.5 billion of foreign oil in 2015.