Centrica, which owns the British Gas brand, has said it is to buy stakes in four North Sea oil and gas fields from Kerr McGee for £318.6m ($567m).
Kerr McGee is upgrading its oil and gas portfolio
The gas and electricity supplier is to buy interests in the Andrew, Brae, Buckland and Skene fields.
The deal should add around 1.1 billion therms of gas and 11 million barrels of oil to its portfolio, the firm added.
Centrica said it was part of its "wider international strategy to secure future supplies" for British Gas customers.
"As the UK becomes a net importer of gas, it is essential that Centrica is able to source gas from a wide and diverse range of options," said Sir Roy Gardner, chief executive of Centrica.
Gas from Brae, Buckland, and Skene is exported to the St Fergus terminal in the north-east of Scotland, and gas from Andrew delivered to the Teesside terminal.
Centrica recently bought a 20% stake in the Canvey Island liquefied natural gas (LNG) project.
Centrica will own 6.66% of BP-operated Andrew, 8% of Marathon-operated Brae, and a third of Buckland and Skene, both run by Exxon Mobil.
Kerr McGee is one of the largest US-based independent oil and natural gas exploration and production companies.
The Oklahoma-based firm also announced on Monday that it was selling its larger North Sea oil assets to Danish shipping giant AP Moeller Maersk for $2.95bn.
"These transactions enhance our strategic plan to high-grade our oil and gas portfolio to focus on assets that have the greatest growth opportunities," said Luke R Corbett, Kerr McGee chairman and chief executive.