As a result of strong oil prices and technology advances making domestic shale resources accessible, the US oil and gas industry had a banner year for growth across several categories. Combined exploration and development spending increased 38% in 2011, according to Ernst & Young's annual US E&P benchmark study. Oil reserves grew by 9%, or 1.7 billion barrels, in 2011, while oil production increased 3%. Gas reserves and production rose 4% and 9%, respectively in 2011. Oil and gas revenues experienced 23% growth in 2011.