The United States produced an average of 6.5 million barrels of crude oil per day in September—the largest monthly average since January 1998, according to the Energy Information Administration. As shown in the chart below, the monthly average has risen by about a million barrels per day since July of of last year. The EIA reports that “most of that increase is due to production from oil bearing-rocks with very low permeability.” The development of hydraulic fracturing and horizontal drilling technologies has made the extraction of oil from such resources much more economical in recent years. These technologies are the main reasons the International Energy Agency expects oil production by U.S. to surpass that of Saudi Arabia within a decade. (See Shale Oil Will Boost U.S. Production, But It Won’t Bring Energy Independence)