Several billion barrels of oil in shale rocks were found under large parts of southern England, said the British Geological Survey (BGS) on Friday.
The study by the BGS assessed the resources of the Jurassic shales of the Weald covering areas including Sussex, Hampshire, Surrey and Kent. It estimated that the range of shale oil in place was between 2.2 and 8.57 billion barrels or 293 and 1,143 million tonnes. The central estimate for the resource was 4.4 billion barrels or 591 million tonnes.
By way of comparison, the equivalent of around 45 billion barrels of oil had been extracted from the North Sea over the past 40 years.
The BGS said the figure for oil represented the total amount of oil present in the rocks. It was not known what percentage of the oil present in the shale could be commercially extracted. In order to estimate the shale oil reserve, drilling and testing of new wells would be required to give a better idea of oil production rates, it added.
But getting the oil out of the ground would involve the controversial process known as fracking. The fracking process involved pumping water, sand and chemicals into rock at high pressure, which could cause pollutions and earthquakes. It has sparked demonstrations by environmentalists.
The British government had given fracking the green light after a supply chain report published in April showing huge potential economic benefits to the country's economy.