The agreement comes after the sale was blocked to two Chinese companies, a Sonangol spokesman told Reuters.
Earlier in the month, a Marathon Oil spokesman told the news agency that due to confidentiality agreements the company could not comment on where the Angola asset sale stood.
US-based Marathon is still believed to want a 10% interest in the block.
Sonangol, which owns 20% of the block, said earlier this month that it had exercised the right of first refusal over Marathon’s decision to sell the stake to Chinese state-owned companies CNOOC and Sinopec, reported Reuters.
This right allows it to step in as the buyer for the price the Chinese companies had offered: $1.3bn.
Production at Angolan Block 32 is expected to start in 2012 and could yield 1.5 billion barrels of oil reserves.