Sydney, Jan 25 (IANS/EFE): A shale formation containing up to 233 billion barrels of petroleum was found in central Australia by Linc Energy, media reports said Thursday.

Linc said reports from two independent consultants confirmed the existence of the non-conventional oil deposits in Arckaringa basin in South Australia, the ABC network reported.

Shale oil, which was difficult to extract just a few years ago, is produced by using hydraulic fracturing, or "fracking".

Fracking is controversial and involves pumping a pressurized fluid - usually composed of water, sand and chemicals - into the shale formation to create a fracture in the rock layer and release trapped petroleum or natural gas.

The process has been used in the US for about three decades, but new technologies have allowed energy companies to reach oil and gas deposits that were previously inaccessible.

Environmentalists oppose hydraulic fracturing on the grounds that it pollutes the soil and aquifers.