The US average gasoline consumption is about 73.3 billion liters per week. Calculating for 10% ethanol and converting to mass (the density and mass of ethanol are easily found) about 53.27 billion metric tonnes/year. This statistic can be easily verified by simple calculations with the available figures on sites such as http://www.epa.gov/.
The 73.3 billion liters per week statistic is from 2004, and gasoline consumption has steadily increased since then. Therefore, by my estimation, the correct number should be somewhere around 77 billion liters per week.