“There are two reasons for this increase in proved reserves. The first is that despite >150 years of oil production in the U.S., new fields are still being discovered. In March 2015 the EIA released its update to the Top 100 U.S. Oil and Gas Fields as a supplement to the December report. This was the EIA’s first update on the Top 100 fields since 2009. The most significant addition to the list was the Eagleville field (in the Eagle Ford Shale), which was only discovered in 2009 but is now the top producing oil field in the U.S. In addition to the Eagleville, there were 4 other fields in the Top 100 that were only discovered in 2009. Several others in the Top 100 were discovered in 2007 and 2008.”

Source: oilprice.com