Shanghai: PetroChina, China's largest oil and gas producer, became the world's first trillion dollar company on Monday after floating on the Shanghai stock market.

Shares in PetroChina more than doubled in their market debut after it raised $9 billion in the world's biggest IPO this year, surging past analysts' expectations as crude prices neared $100.

China's top oil producer has doubled the capitalisation of the second biggest company, rival oil giant Exxon Mobil, at $488 billion.

PetroChina executives, investment bankers and brokers cheered at the Shanghai Stock Exchange as the stock's opening price of 48.60 yuan flashed on an electronic screen.

Government-controlled PetroChina closed at 43.96 yuan in Shanghai, up 163 per cent from its IPO price and far above analysts' forecasts of around 35 yuan, underlining investor confidence in China's red-hot economy and PetroChina's status as its biggest oil and gas producer.

But the massive demand for PetroChina shares was partly due to wild speculation that has gripped China's stock market during a bull run that began last year, analysts said. That could hurt the stock and the overall market later on.

"The opening price is really too high as far as PetroChina's corporate fundamentals are concerned," said industry analyst Wang Jing at Orient Securities in Shanghai, adding that many investors were piling into the stock as a short-term trade rather than a long-term investment.

Analyst Dong Yong at Haitong Securities said surging global oil prices, which hit an all-time high above $96 a barrel in New York last week, were good news for PetroChina so far. Last week, Beijing hiked domestic fuel prices by up to 10 per cent.