BEIJING -- Sinopec, China's top oil refiner, on Wednesday defended itself against online complaints alleging that the company's 93 RON gasoline was diluted and caused vehicles to malfunction.

"The company's oil products have met the national standard and there is no quality problem," an official from the company's publicity department told Xinhua.

The remark came in response to online complaints that alleged China's two oil giants, Sinopec and PetroChina, are diluting the widely-used 93 RON gasoline in order to cut costs. These complaints also claimed the "questionable" gasoline caused vehicle engines to malfunction.

Sinopec spokesman Huang Wensheng said the company only received one complaint from a consumer in Yuxi, Yunnan province, last week. But the consumer rescinded the complaint after an inspection confirmed that the reported problem was not caused by the fuel.

Last week, Chinese netizens posted pictures of bottled 93 RON gasoline from the two companies, which were of two different colors, sparking speculation that the products had been diluted.

The color of gasoline is not an essential standard for judging its quality, said Nie Hong, deputy director of Sinopec Corp Research Institute of Petroleum Processing.

On Wednesday, Sinopec's stocks fell 1.04 percent to 7.62 yuan ($1.21) per share, while PetroChina inched down 0.75 percent to 10.52 yuan at the Shanghai Stock Exchange.