U.S. oil production, including crude oil and lease condensate, has grown steadily since 2008, a change from the two decades of declines before 2008. This growth has been driven mainly by increased production from various tight (very low permeability) formations. (Permeability measures how well liquids and gases can flow through open spaces in rocks.) Horizontal drilling combined with hydraulic fracturing have allowed exploration and production (E&P) companies to access commercial volumes of oil from rock formations that are less permeable than those found in conventional formations. The U.S. Energy Information Administration (EIA) expects that development of tight formations will lead to continuing significant increases in U.S. oil production in the coming years.