HRT will take on a 60% stake in the Campos Basin field from the UK supermajor, where Denmark's Maersk is on 40%.
HRT and BP signed a purchase agreement for $135 million in May but the amount went down after a "purchase price adjustments", HRT said in a statement on Thursday.
The Brazil firm, stung by disappointing results off Namibia and onshore Brazil, will also take a 100% interest in the holding company that owns the Polvo A platform and a 3000-HP drilling rig assigned to the field, it said.
HRT
