China’s net exports of gasoline doubled in the first half of this year amid a fuel surplus in the country, the world’s second-biggest oil consumer.

Overseas sales of gasoline exceeded imports by 2.5 million metric tons from January to June, according to Bloomberg calculations based on data e-mailed by the General Administration of Customs in Beijing today. That’s equivalent to 116,400 barrels a day. Net exports of the motor fuel were about 1.3 million tons over the same period in 2012.

“Refiners were exporting more because there’s a surplus of domestic fuel supply,” Li Li, an oil analyst at ICIS-C1 Energy, a Shanghai-based consultant, said by phone from Guangzhou.

China is experiencing an oversupply as refiners produce fuels at a faster rate than demand is growing, amid a slowdown in Asia’s largest economy. Gasoline output climbed 14 percent over the first six months to 48.85 million tons, according to the National Bureau of Statistics. By comparison, apparent demand for the motor fuel gained 12 percent over the same period, the National Development and Reform Commission said on July 19.

Gasoline exports from this month to December may slow as refiners including PetroChina Co. and China Petroleum & Chemical Corp. (386) have exhausted their sales quotas and the government hasn’t decided to increase allocations, according to Li.

Net exports of diesel in the first half reached 1.5 million tons, or almost 62,000 barrels a day, according to the data. In the same six-month period last year, the country was a net importer of 61,205 tons.