As of 2009, motor vehicles used most of the petroleum consumed in the U.S. and produced over 60% of the carbon monoxide emissions and about 20% of greenhouse gas emissions in the United States, however production of hydrogen for hydro cracking used in gasoline production chief amongst its industrial uses was responsible for approximately 10% of fleet wide greenhouse gas emissions. In contrast, a vehicle fueled with pure hydrogen emits few pollutants, producing mainly water and heat, although the production of the hydrogen would create pollutants unless the hydrogen used in the fuel cell were produced using only renewable energy.