WASHINGTON (AFP) - The United States expanded its lead as the world's largest producer of oil and natural gas last year as production from fracking fields surged with US output now about double that of Saudi Arabia, the US Department of Energy reported Tuesday.

While hydrocarbon production in Russia and Saudi Arabia remained relatively flat, US output, by the British thermal unit (Btu) measure of energy content, gained about 10 per cent to nearly 55 quadrillion Btu last year.

That increase represented a 1.6 million barrel a day rise in crude production and a 13.9 billion cubic feet a day rise in natural gas production.

US production is evenly split between crude oil and natural gas, according to the EIA. In Russia output is also balanced between oil and gas, while Saudi Arabia mainly produces crude oil.

The US production gains came despite a 50 per cent fall in oil prices during the second half of the year, the EIA noted.