A gasoline Golf gets 28 mpg (see note 1)
A diesel Golf gets 41 mpg (see note 1)
Biodeisel gets 15% lower mileage than diesel (see note 2)
Ethanol get 33% lower mileage than gasoline

One acre of soybeans produces 62 gallons of biodiesel
One acre of corn produces 385 gallons of ethanol.

28 * (1-0.33) =18.8
41 * (1-0.15) =34.9
385/62 * 18.8/34.9  = 3.3 more acres to grow the same "mileage" of biodiesel as corn.

Note 1:http://www.epa.gov/emissweb/smcar-06.htm

Note 2: http://www.cytoculture.com/Biodiesel%20Handbook.htm

In the Southwest Research Institute study (1996), the fuel consumption was found to increased by 14% when Biodiesel was used at 100% in the Cummins test engine operated under transient heavy loads

In testing Biodiesel in the CytoCulture Mercedes Benz diesel station wagon over the past 4 years, there was about a 15% net decline in the mileage obtained using neat Biodiesel

These local observations were confirmed by the 1998 engine performance studies at the Southwest Research Institute. Fuel consumption in a 1995 Cummings B-5.9 truck engine increased by 18% with the neat Biodiesel.

For a 1997 Cummings N-14 truck engine a 13% increase in fuel consumption wast noted with the neat Biodiesel.