Diesel contaminates much more than gasoline. So diesel is is almost only used on 18-wheelers, who don't care much about being green. Remember that maintenance costs for biodiesel is way higher than straight diesel, so freight companies aren't interested. But biogasoline would be a smash hit! First it would be almost tax-free. Second cars (and its drivers) aren't that demanding, they would redily buy biogasoline if they could just pour it into their gas tanks without modifications to their cars.