It will see French firm Total take control Denmark's Maersk's assets in the UK sector of the North Sea, including the Culzean gas field.
Total said an "exceptional overlap" of businesses would increase its competitiveness through growing assets and annual cost-savings.
The deal will require the approval of regulators.
Total chairman and chief executive Patrick Pouyanne said: "The combination of Maersk Oil's North Western Europe businesses with our existing portfolio will position Total as the second operator in the North Sea with strong production profiles in UK, Norway and Denmark."
Energy company Total has agreed to buy Maersk's oil business in a $7.45bn (£5.8bn) deal.