Reaching their highest levels in 60 years, alternative fuels led by biomass-based fuels and natural gas last year accounted for 8.5% of the transportation fuel mix, the U.S. Energy Information Administration (EIA) reported Monday.

The share of fuels other than petroleum for U.S. transportation has increased to its highest level since 1954, EIA said in its “Today in Energy” report. Natural gas has reached a historic high in the process, but that includes its use in pipeline and vehicular transportation.

“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,” according to EIA analyst Ryan Repice.

After about 50 years at the 4% level, non-petroleum sources of fuel for transportation — biomass products, natural gas and electricity — began to account for a larger share about 10 years ago and have climbed steadily to account for 8.5% of the transportation fuel collectively last year, EIA data reveal.

Last year, natural gas transportation fuel use reached a historic high of 946 trillion Btus, representing 3.5% of all the gas used in the United States, EIA said. Natural gas used to fuel vehicles has more than doubled since 2000, although it is still the smallest amount of transportation natural gas, which is mostly used to operate pipeline compressor stations.

Fuel ethanol has grown the fastest in recent years among the non-petroleum transportation fuels, EIA said. It increased by nearly one quadrillion Btus during the last 15 years, with nearly all of the ethanol being blended into gasoline in quantities of 10% or less. Consumption of biodiesel in 2014 grew to more than 180 trillion Btus, mostly in trucks and buses.

During the same 15-year period, electricity sales to the transportation sector grew more than 40%, although sales have declined slightly since 2007, according to the EIA report.

“The increase does not include the power consumption in electric vehicles that are not used in mass transit, because charging stations for these types of vehicles are likely associated with meters on residential, commercial or industrial customer sites, where this specific use may not be differentiated from other uses,” Repice said.