The deal also includes prospects in Azerbaijan and deepwater sites in the Gulf of Mexico, with 10 exploration blocks, mainly in the Campos Basin.
BP will also get Devon's 30 per cent stake in the Kaskida field in the Gulf of Mexico, in which BP already owns 70 per cent.
The acquisition will allow BP to begin exploring off the coast of Brazil, which is expected to boost the group's potential reserves by about 2bn barrels of oil.
BP will also sell Devon half its stake in the controversial Kirby oil sands in Alberta for $500m. The two companies have agreed to form a 50-50 joint venture to develop the Canadian project which is not yet under production.
The purchase of Devon's Azeri-Chirag-Guneshli (ACG) development in Azerbaijan, worth an estimated $3bn, raises BP's stake to just under 40 per cent. ACG represents 1 per cent of global crude production, with an output of 820,000 barrels per day.
Tony Hayward, BP chief executive, said the Devon assets are a good fit for BP.
The purchase is BP's biggest acquisition since the oil giant invested $8bn in its Russian joint venture, TNK-BP, in 2003.
