Next, the researchers looked at how much it would cost to achieve governmental targets for biofuel use and what the impact would be on fossil fuel use. In the U.S., the Renewable Fuel Standard calls for 15 billion gallons of conventional biofuel sources such as corn ethanol; 1 billion gallons of biomass-based diesel; 16 billion gallons of advanced cellulosic biofuels; and 4 billion gallons of other advanced biofuels to be used in transportation fuel by 2022. U.S. corn ethanol production has already reached 13 billion gallons, Jaeger said, but cellulosic ethanol, a so-called second-generation biofuel, is not yet commercially produced in the U.S.

The researchers concluded that all of these biofuel mandates combined would reduce fossil fuel use by less than 2.5 percent, or the same amount that a gas tax increase of 25 cents per gallon could achieve, but at an estimated cost of $67 billion compared with a cost of $6 billion with a gas tax.

To directly compare the cost-effectiveness of the biofuels with the two alternative approaches, part of the researchers’ analysis evaluated the biofuels in combination with forest carbon sequestration practices so that they would produce the same mix of reductions in fossil fuel use and greenhouse gas emissions as a gas tax increase.

The study did not take into account the effect that increased production of biofuels might have on water use, pollution and food prices, all of which raise additional concerns about the merits of promoting biofuels, according to Jaeger.

The study is called Biofuel Economics in a Setting of Multiple Objectives and Unintended Consequences and was published in Renewable and Sustainable Energy Reviews. The study can be downloaded at