Foreign firms, hungry to cash in on the American energy boom, have invested nearly $6 billion in U.S. gas and oil drilling in the last few weeks. Energy giants from China, France and Spain have snapped up stakes in fields in Ohio, Mississippi, Colorado and Michigan. These investments will likely add to the recent boom in U.S. natural gas production, pushing already low natural gas prices even lower. Low domestic prices could drive natural gas producers to seek out European and Asian markets, according to analysts, where the fuel commands three or four times the price. “Of course that will” lead to more exports, said Nansen Saleri, president of the oil field consulting firm Quantum Reservoir Impact. “And it will be a tremendous opportunity.”