GUANGZHOU, China  Auto sales are so strong in China that an unusual conspiracy theory has circulated on Western stock markets this month: the Chinese government must be secretly buying hundreds of thousands of cars and parking them somewhere.

The main evidence presented for the theory is that the number of gallons of gasoline consumed in China has been flat this year. But auto executives and Chinese buyers deny the rumor, which has spread so widely that economists have begun producing reports on why it is implausible.

Kevin Wale, the president of General Motors China, said that automakers knew who was buying their cars and saw no evidence of a car-buying conspiracy. Sharp improvements in fuel economy  partly because of government mandates and partly because of a shift to smaller cars  help explain the slow growth in gasoline sales, he said.

A series of recent increases in regulated fuel prices may have also discouraged some driving, he added.