Image caption Shale oil and gas is now big business in the US

The US will overtake Saudi Arabia as the world's biggest oil producer "by around 2020", an International Energy Agency (IEA) report has said.

The IEA said the reason for this was the big growth and development in the US of extracting oil from shale rock.

This has enabled the US to gain significantly more extractable oil resources.

As a result, the IEA predicts the US will become "all but self-sufficient" in its energy needs by around 2035.

The US shale oil industry has grown significantly in recent years.

It extracts oil from the ground using a method called fracking - pumping down a mixture of sand, water and chemicals at high pressure.

The industry says the method is safe, but critics say it could cause earthquakes and pollute water sources.

The IEA predicts that the US will be producing 11.1 million barrels per day by 2020, compared with 10.6 million from Saudi Arabia.

Currently the US imports about 20% of its total energy needs.

The IEA also expects that the US will overtake Russia as the world's biggest gas producer by 2015, again thanks to fracking, which can also be used to extract natural gas.

It warns that the big growth in US oil and gas production could have significant geopolitical implications, as it may make the US less concerned about the Middle East.