China refiners sold just under 500,000 tonnes of gasoline in August.
"September is still a good month for gasoline demand in China. Things won't slow down until early October," a Singapore-based source said.
Car sales in China rose 1.6 percent in July from June to snap a three-month decline, according to official data released earlier this month by China Association of Automobile Manufacturers.
Analysts expect car sales this year may grow about 10 to 20 percent versus 2003, when sales almost doubled to about 2 million.
China's gasoline consumption also tends to rise around late September ahead of the country's National Day holiday, which is celebrated during the first week of October.
"Local demand has forced refiners to cut exports.
Demand is quite robust," said a trader.
PetroChina will export just 90,000 tonnes of gasoline for September after selling as much as 210,000 tonnes in August, sources said.
Sinopec Corp will export 150,000 tonnes of the motor fuel for September, down from 190,000 tonnes sold for August. More than half of Sinopec's gasoline supply is bound for Vietnam, sources said.
Export-oriented refiner West Pacific Petrochemical Co Ltd has agreed to sell 120,000 tonnes of gasoline for September.
Benchmark Singapore gasoline prices for 92-octane supply have also fallen more than 14 percent in the past week to about $46.75 a barrel due to softer crude oil futures, giving refiners less of an incentive to export supply.