http://apps.washingtonpost.com/g/page/national/unexpected-loose-gas-from-fracking/950/

A survey of hydraulic fracturing sites in Pennsylvania revealed drilling operations releasing plumes of methane 100 to 1,000 times the rate the EPA expects from that stage of drilling, according to a study published Monday in the Proceedings of the National Academy of Sciences.

Natural gas as an energy source for electric-ity production is less of a contributor to global warming than coal only if less than 3.2 percent of methane escapes during production. Recent measurements estimate that between 2.3 percent and 17.3 percent of gas escapes.