Statoil's chief executive Helge Lund unexpectedly resigned today to take the top job at smaller rival BG Group, the firms said in separate statements.
Lund leaves state-controlled Statoil after more than ten years in the top job.
The firm has appointed Eldar Saetre, its current head of marketing, processing and renewables division, as its acting chief while it searches for a new CEO.
"Lund has built a world-class exploration and production portfolio at Statoil, and the company is now widely admired for its technical expertise, financial performance and strong, values-based culture," BG chairman Andrew Gould said.
Lund expanded Statoil from a mostly domestic firm to an international major with a $77.5 billion market capitalisation and an international exploration and production portfolio spanning from Brazil to Indonesia.
Under Lund, the firm has also become one of the most successful explorers, with big finds in places like Canada, Brazil and Tanzania.
But Lund also leaves at a difficult time as the firm cuts capital spending plans, lays off workers and cuts costs after oil prices slumped to a four-year low and cost inflation squeezed margins.
