China's sovereign wealth fund China Investment Corp (CIC) and state refiner Sinopec are among the three cornerstone investors to pledge $350 million toward Canadian oil explorer Sunshine Oilsands Ltd's Hong Kong IPO, Reuters reported, citing a source with direct knowledge of the matter.

The three institutions are taking up nearly half of Sunshine Oilsands' planned $700 million initial public offering (IPO), the source told Reuters on Tuesday. The offering will be the biggest stock market float in the world so far this year.

CIC and China Petrochemical Corp (Sinopec Group), parent of listed China Petroleum & Chemical Corp (Sinopec), have each agreed to buy $150 million worth of shares in Sunshine Oilsands, the source said.

Washington-based asset manager EIG Global Energy Partners pledged $50 million, the source added.

Cornerstone investors back many Asian listings, committing to buy large, guaranteed stakes and agreeing to a lock-up period during which they will not sell their shares.

The source was not authorized to speak publicly about the matter. Both CIC and Sinopec were not available for immediate comment. Sunshine and EIG could not be reached immediately.

The IPO will consist of all new shares, representing 25 percent of the company's expanded capital, one source with direct knowledge of the plans previously told Reuters.

Calgary-based Sunshine Oilsands owns 1.14 million acres of oil sand leases in the Athabasca region in Canada's Alberta province.

The company and its bankers started drumming up demand for the offering on January 30. They are expected to start a roadshow to take orders on the deal on February 15 or possibly a week later, the source added.

Sunshine Oilsands had raised about $230 million in March last year from a group of investors including a unit of Bank of China, China Life Insurance (Overseas) and Hong Kong private equity fund Cross-Strait Common Development Fund.

Sunshine's IPO will be the first major share sale to get off the blocks in Hong Kong in what is expected to be another slow year for IPOs after demand for new listings slumped 42 percent in 2011 from the year before.

A handful of companies have gone public in Hong Kong since the beginning of the new year, with small-sized deals that raised a total of about HK$1.4 billion ($181 million).

Other new listings around the world have also lagged behind the mega offerings seen in 2011, with oil producer RusPetro taking the top spot so far with at $250 million from its London IPO last month.

BOC International, Deutsche Bank and Morgan Stanley were hired as joint global coordinators and joint sponsors of Sunshine's IPO.