Exxon bought the shares for $1.59 each during Sinopec's initial public offering in October 2000, and stands to make a profit of up to $6.13 billion from the sale. Final pricing was not expected until this morning as the deal was still open to investors in the United States.

Exxon's disposal marks the end of the foreign oil majors' strategic investments in their mainland peers, which were made with an eye towards paving the way for larger-scale co-operative investments in China's market.

For the most part, such opportunities never materialised, with the absence of foreign participation in China's massive east-west national gas pipeline perhaps the largest disappointment. The overseas oil majors have instead limited investments to a handful of massive downstream ethylene projects and provincial retail gas joint ventures.

The overseas oil majors at least reaped a tidy return on what turned out to be prescient portfolio investments.

Exxon, along with BP and Shell, supported Sinopec's dual Hong Kong and New York offering in October 2000. Shell sold out in March last year, booking a profit of more than $2.8 billion on its original investment.

This followed in the heels of BP in February, selling its Sinopec shares at a 98 per cent premium to their issue price.

BP also bought 20 per cent of PetroChina's Hong Kong public offer in April 2000. It sold its stake in January last year, reaping a 184 per cent gain on its investment.

ExxonMobil is believed to have held out the longest mainly for strategic considerations. It was only in August last year that it concluded talks with Sinopec and Saudi Aramco for a US$3.5 billion refining and petrochemical project in Fujian province.

'ExxonMobil hung on to the shares because it was still in negotiations with Sinopec on the Fujian project,' said UOB Kay Hian analyst Michael Lee Ho-cheung. 'The share disposal should clear the share price overhang for Sinopec and will narrow its valuation gap with PetroChina.

'In the short term, the share price may come under pressure from the placement,' said Phillip Securities director Louis Wong Wai-kit. 'But in the long term, it should continue to do well as most analysts forecast the robust demand for oil and petrochemical products in China to continue.'

The shares on offer accounted for about 18.9 per cent of Sinopec's outstanding H shares and could have a big impact on trading as the size of the offer was equal to Sinopec's average trading volume over a 42-day period, one source said.

The stock has risen 42 per cent from last year's low in May, in tandem with last year's rally in oil prices, and is up 7.6 per cent over the past three sessions as snowstorms in the US and Europe have driven crude prices above US$50 a barrel. But the stock has not reached the record high of $3.85 seen on January 2 last year.