London-listed Savannah Energy has agreed to buy producing oil fields in South Sudan from Malaysia's state energy firm Petronas for up to $1.25 billion, it said.
The announcement followed Exxon Mobil Corp closing a $407 million sale of its operations in Central Africa's Chad and Cameroon to Savannah.
China's CNPC and Sinopec, India's ONGC, and South Sudan's national oil company, Nilepet, are also shareholders in the South Sudan fields, which have a gross output of 153,000 barrels per day.
A spokesman declined to provide a net production figure for the stakes Savannah wishes to purchase.
The transaction, which is still subject to shareholder and regulatory approval, is a reverse takeover because the assets are larger than the company acquiring them.
"The Transaction Consideration is expected to be financed through a combination of the enlarged Group's available cash resources and debt," Savannah said in a statement, implying that the final amount of cash paid will be determined by the closing date of the deal.
Savannah Energy follows the Chad acquisition with a South Sudan acquisition.