The Prius sold about 15,000
The Prius sold about 15,000 annually nationwide in its second year (2001) in the US. The Volt is at 13,000 with three months to go in its second year.
p.s Toyota got subsidies for fuel efficient cars from Japan, there is no such thing as "free market", at least not yet.
Toyota sells more than 10,000 Prius vehicles a MONTH now in the US.