PetroChina Co passed Exxon Mobil Corp on Thursday as the biggest energy company by market value for the first time since 2010.

Exxon's capitalization was $352.6 billion through Wednesday, compared with PetroChina's $352.8 billion on Thursday in Shanghai.

The Chinese company's A shares have surged about 61 percent the past year, versus Exxon's 14 percent drop. PetroChina was larger by value most recently at the close of trading on June 25, 2010, data compiled by Bloomberg show.

The Shanghai Composite Index has gained about 88 percent over the past year, the best performance among major indexes tracked by Bloomberg, amid speculation the central bank will extend cuts in borrowing costs and on increased use of leverage to buy stocks.

The Chinese yuan has declined 0.1 percent versus the dollar the past year even as most currencies weakened.

"PetroChina has multiple positives at the moment: it's got a reform story, it's also listed in Hong Kong, and China has more freedom for mainland fund managers in the works," said Mark Matthews, head of Asia research and managing director of Bank Julius Baer & Co in Singapore.

"China is also planning to transfer stakes in State-owned enterprises away from their regulator, which will on the whole be positive for SOEs."

Earnings of both companies have been squeezed by the plunge in the price of oil. Exxon's adjusted net income of $6.3 billion in the fourth quarter was the lowest since a loss in the final three months of 2009, according to data compiled by Bloomberg.

PetroChina's profit was 11.1 billion yuan ($1.8 billion) in the same period.