The US Geological Survey (USGS) has announced the discovery of the largest deposit of oil and gas in US history.

Found in west Texas, the record-breaking energy reserve is located in what's known as the Midland Basin portion of the Permian Basin.

Early reports suggest it could hold up to 20 billion barrels of oil and 16 trillion cubic feet of gas. Based on the current price of $45 for a west Texas barrel of crude oil, this gives the deposits an estimated value of around $900 billion.

That is three times the amount forecast in the last major oil and gas discovery made in the US in 2013.

The Bakken Shale in North Dakota was considered to be the largest find of unconventional oil ever discovered, and has since propelled the mid- western state into the second biggest energy producer in the country.

For decades prospectors have been surveying the oil and gas fields around the city of Midland, located in the southern plains of west Texas. The most recent discovery, however, was made in an area known as the Wolfcamp Shale, which had heretofore not been considered as valuable as other nearby areas.

Out of reach

However, since horizontal drilling and hydraulic fracturing – or ‘fracking’ – have become standard industry practice, reserves that were previously out of reach have become accessible.

"The fact that this is the largest assessment of continuous oil we have ever done just goes to show that even in areas that have produced billions of barrels of oil there is still the potential to find billions more," said Walter Guidroz, programme co-ordinator for the USGS energy resources programme.

"Changes in technology and industry practices can have significant effects on what resources are technically recoverable, and that's why we continue to perform resource assessments throughout the United States and the world."

According to the US Energy Information Administration, the United States has been producing more oil and natural gas than any other nation every year since 2012.