GM is expected to show a sales increase of 15.3% from a year ago when it posts August numbers later this week, according to auto industry research firm Edmunds. That would be an improvement of 30,000 cars and light trucks and would eclipse the unit gains of its smaller rivals.
Short sellers have significantly increased their bet that GM shares are going to drop: Short interest in the No.1 U.S. car company jumped 26.5% to 41.5 million shares in the two-week period that ended May 15.
Car prices have risen quickly and quietly in the last few weeks. According to auto industry research firm Edmunds, the average amount buyers are paying for cars or light trucks is up $350 since Japan's earthquake and tsunami in March -- and the price of Japanese vehicles is up even more.