Replacing all the transport fuel consumed in the
United States with biodiesel will require 0.53 billion m3
of biodiesel annually at the current rate of consumption.
Oil crops, waste cooking oil and animal fat cannot
realistically satisfy this demand. For example, meeting
only half the existing U.S. transport fuel needs by
biodiesel, would require unsustainably large cultivation
areas for major oil crops. This is demonstrated in
Table 1. Using the average oil yield per hectare from
various crops, the cropping area needed to meet 50% of
the U.S. transport fuel needs is calculated in column 3
(Table 1). In column 4 (Table 1) this area is expressed as
a percentage of the total cropping area of the United
States. If oil palm, a high-yielding oil crop can be
grown, 24% of the total cropland will need to be devoted
to its cultivation to meet only 50% of the transport fuel
needs. Clearly, oil crops cannot significantly contribute
to replacing petroleum derived liquid fuels in the
foreseeable future. This scenario changes dramatically,
if microalgae are used to produce biodiesel. Between 1
and 3% of the total U.S. cropping area would be
sufficient for producing algal biomass that satisfies 50%
of the transport fuel needs (Table 1). The microalgal oil
yields given in Table 1 are based on experimentally