Mitigation of peak oil is another alternative, and combined cycle power generation using natural gas is the cleanest source of power available using fossil fuels, producing about 30% less carbon dioxide than burning petroleum and about 45% less than burning coal. The major difficulty in the use of natural gas is transportation and storage because of its low density. Natural gas pipelines are economical, but are impractical across oceans. Due to its high energy density and ease of handling, oil has a unique role as a transportation fuel. There are, however, a number of possible alternatives. Among the biofuels the use of bioethanol and
Natural gas in the United States the oil and the gas are treated separately. Gas flows through a gathering system into a pipeline to a gas processing plant. As of 2014, there were 189,000 miles of interstate natural gas pipelines in the United States Natural gas has a variety of chemical constituents that must be removed or diluted with other gas to achieve consistent pipeline quality. Pipeline gas specifications vary from line to line, but generally the gas must contain no appreciable hydrogen sulfide (which is toxic), less than a few percent carbon dioxide (carbon dioxide reacts with water to form carbonic acid, which is corrosive