FILE - In this Sept. 4, 2008, file photo, Garvin Cui fuels up his natural gas vehicle at a Clean Energy station in San Francisco. New technology has unlocked vast reserves of natural ga

 

              FILE - In this Sept. 4, 2008, file photo, Garvin Cui fuels up his natural gas vehicle at a Clean Energy station in San Francisco. New technology has unlocked vast reserves of natural ga
FILE - In this Sept. 4, 2008, file photo, Garvin Cui fuels up his natural gas vehicle at a Clean Energy station in San Francisco. New technology has unlocked vast reserves of natural gas in deep rock formations, creating a natural gas glut that has depressed prices. That makes natural gas more attractive as a transportation fuel. (AP Photo/Marcio Jose Sanchez, File)