In the United States, petroleum is by far the most-consumed transportation fuel. But recently the share of fuels other than petroleum for U.S. transportation has increased to its highest level since 1954, a time when the use of coal-fired steam locomotives was declining and automobile use was growing rapidly. The recent increase can be mostly attributed to increased blending of biomass-based fuels with traditional vehicle fuels and growing use of natural gas in the transportation sector. After nearly 50 years of relative stability at about 4%, the nonpetroleum share started increasing steadily in the mid-2000s, reaching 8.5% in 2014. Of the nonpetroleum fuels used for transportation, fuel ethanol has grown most rapidly in recent years, increasing by nearly one quadrillion British thermal units (Btu) between 2000 and 2014. […]