Other shareholders in the South Sudan fields, which have a gross output of 153,000 barrels per day, include China's CNPC and Sinopec, India's ONGC and Nilepet, the national oil company of South Sudan.
A spokesman did not immediately provide a net production figure for the stakes Savannah wants to buy.
The deal, which still needs shareholder and regulatory approval, constitutes a reverse takeover because the assets are bigger 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, meaning the final amount of cash paid depends on the deal's closing date.
Savannah's market capitalization on London's AIM market stood at around 353 million pounds ($433.31 million) on Monday.
Savannah's shares were suspended from trading on Monday and will resume once a detailed document for the transaction has been published, which the company expects to happen in the first half of next year.