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HOUSTON (Reuters) - The largest oil field in the United States holds as much as 49 years worth of oil at current production rates, according to data from a report released on Thursday by the U.S. Geological Survey (USGS).

In its first assessment of the Delaware portion of the Permian shale field that spans west Texas and New Mexico, the USGS, which is part of the U.S. Department of the Interior, said it contains about 46.3 billion barrels of oil and 281 trillion cubic feet of natural gas.

The government estimates include all underground shale oil and gas that is technically recoverable but may not be economic to extract at current prices.

The estimate is twice the size of the country’s next largest shale reserve - the Midland Basin - another portion of the Permian. In 2016, that was found by the USGS to have about 20 billion barrels of oil and 16 trillion cubic feet of natural gas.

Survey results “demonstrate the impact that improved technologies such as hydraulic fracturing and directional drilling have had on increasing the estimates,” said Walter Guidroz, an official in the USGS Energy Resources Program. Hydraulic fracturing forces water and sand underground at high pressure to free oil and gas trapped in shale rock.

The Permian Basin, which includes both shale regions, is expected to pump 3.7 million barrels of crude oil per day this month, up 30 percent from a year ago, according to the U.S. Energy Information Administration.

The Delaware and Midland basins combined would take 49 years to produce if all the oil was profitable to recovery, according to the EIA figures.