The area of Chinese tallow trees needed to supply Australia with its 2006 diesel needs is 18,300 square km which is 0.24% of our land area.
"Registered motor vehicles in Australia consumed 28,898 million litres of fuel in the 12 months ended 31 October 2006.
Of the total fuel consumed by motor vehicles in this period, 65.8% was petrol and 29.8% was diesel."
http://www.abs.gov.au/AUSSTATS/abs@....6?OpenDocument
The area of Australia is 7.74 million sq km and Chinese tallow produces 4700 L of fuel per ha.