I've been doing some sums again, and the more I do these sums the more I think we have to get away from the idea that biofuels can ever be much more than spit in the ocean of gasoline (remind me of that in five year's time someone).
In the US for example the average vehicle (excluding buses and big trucks) consumed 743 gallons of gasoline in 2005 at an average fuel efficiency of 16.7 miles/gallon (US). This equates to consuming 179,100 million gallons (up from 57,880 million gallons in 1960) , according to RITA.
It takes 38lbs (17.41)kg of corn (or an average crop) to produce 1 gallon of US gasoline each year,(taking a conversion factor of 232kg corn to produce 50 litres ethanol from the UN), so each US car would need 28,463 lbs or 14.23 tonnes of crop to cover that mileage 2006. There were 241,194 cars on the road in the US in 2006 so we'd need adjusting for the lower energy density of ethanol about 4.9bn tonnes of harvested crops to match that volume of liquid fuels.The bad news is that the US harvest came in last year at 1.9bn tonnes, which would be enough to keep the US on the roads from January 1 to May 24.
People will say that this is a ludicrous calculation (which it is) and that I've not included the potential of cellulosic ethanol, biodiesel and a range of other factors, (which is true). But there is no mainstream alternative technology to ethanol at the moment.