Unless a major technological breakthrough occurs in the next few years, a U.S. government push to put 16 billions of gallons of cellulosic biofuel into gas tanks annually by 2022 will be a bust, hints a new report.

The push comes from the congressionally mandated Renewable Fuel Standard. Of the mandated total of 36 billion gallons from a mix of biofuels, the corn-derived ethanol target of 15 billion gallons is doable, the report says.