The market share for large fuel-thirsty cars has fallen as petrol prices rise.
In 2004 big saloons made up a quarter of the market - now it's only about 11 percent.
The Motor Industry Association says it sees an increase in purchases of small and medium cars when fuel goes up.
year-to-date figures show the Holden Commodore is in third place, and the Ford Falcon sixth, with the Toyota Corolla being top seller.
However, MIA chief executive Perry Kerr says he does not expect the large market to fall further as car makers continue to invest in technology to make its cars more fuel efficient.