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
Low-carbon power entirely renewable sources. Other options, such as nuclear power, produce a comparable amount of carbon dioxide emissions as renewable technologies in total life cycle emissions, but consume non-renewable, but sustainable materials (uranium). The term "low-carbon power" can also include power that continues to utilize the world’s natural resources, such as natural gas and coal, but only when they employ techniques that reduce carbon dioxide emissions from these sources when burning them for fuel, such as the, as of 2012, pilot plants performing Carbon capture and storage. As the single largest emitter of carbon dioxide in the United States, the electric-power