SINOPEC, China's dominant refining company, has come under fire over the purchase of large quantities of expensive alcohol by one of its subsidiaries.

Photocopies of invoices for drink bought by Sinopec's Guangdong branch were posted on the popular Tianya online forum earlier this week, alongside claims it was used as gifts or for receptions during last year's Mid-Autumn Festival by General Manager Lu Guangyu.

The online post said the company spent 2.59 million yuan (US$396,400) in September last year on hundreds of bottles of fine wine and liquor, including Kweichow Moutai and Chateau Lafite Rothschild. The purchases included 1996 Lafite priced at almost 12,000 yuan a bottle, and 50-year-old Moutai at more than 10,000 yuan a bottle, according to the rubber-stamped invoices.

Sinopec Guangdong confirmed the authenticity of the invoices and said it was investigating the issue, according to Xinhua news agency.

The company also said the purchases had nothing to do with Lu personally but were part of the company's "normal operations."

But it didn't say for what purpose the liquor was used.

Still, the disclosure soon made the company a target of public anger, especially at a time when China's fuel prices are at record high levels after the government raised rates twice this year - a move that benefited Sinopec which has been long lobbying for higher fuel prices, or state bailouts, to compensate for losses caused by soaring prices for crude oil.

"Now I know why fuel prices rose again and again. It's being used to sustain the consumption and luxury life of these company leaders," one online post said.

Others wondered why so much alcohol was involved, raising questions of possible bribery.

This was not the first time that the state-owned Sinopec has run into trouble outside its main business operations this year. In February, the company was embarrassed by disclosures that it used its own employees to pose as average citizens to post online comments supporting a rise in fuel prices.