The rejection of a major energy industry takeover by Canadian government may not indicate that it is adopting a harder line on mergers involving foreign companies.

On Friday, Canada used foreign investment laws to reject a $5.17 billion takeover of Progress Energy Resources by Petronas, the Malaysian state-owned energy company.

That decision led to speculation on the outcome of a $15 billion bid for Nexen, another Canadian energy company, by China National Offshore Oil Corporation, the Chinese state-run oil producer known as CNOOC (pronounced SEE-nook).

The Progress deal was the third foreign takeover turned down by the current Conservative government using a law that previously was mainly known for rubber-stamping acquisitions. All three rejections — the others involved a potash mining company and an aerospace company — were unexpected given the antiregulation bent of the government and Stephen Harper, the prime minister.

The review system was introduced by a Conservative government in 1985 to replace a stronger law introduced in a wave of nationalism in the 1970s. Instead of requiring specific commitments in areas like jobs, technology and Canadian management, the law requires only that a takeover provide a "net benefit" for Canada.

But net benefit is not clearly defined in the law. Instead, it is defined on a case-by-case basis, with the prime minister as the final judge. Calls from investors and businesses recently led the Conservatives to start developing clearer guidelines, which it will make public. That process may also have led to the rejection of the Progress deal.

Although Canada's foreign investment review process is secretive and political, it appears that impatience by Petronas, rather than the merits of its bid, led to the rejection on Friday. And that rejection is not the last word in this case.

The Globe and Mail and The National Post, citing unnamed sources, reported said that the government initially promised Petronas a decision by last Friday. But, according to the newspaper reports, the government asked Petronas last week if it could delay its decision until December so that it would follow the release of its new, broad foreign takeover guidelines.

Petronas, the reports said, was already frustrated by the process and any further delay would complicate deadlines under its agreement with Progress. So it turned down the government's extension request. The rejection followed.

After the deal was rejected, however, the government indicated that the process was not over. And on Monday, Petronas and Progress said in a statement that they would continue to work with the government to try to get their deal approved.

Politics aside, the Nexen deal with CNOOC faces different hurdles than the Petronas offer.

Although Nexen's assets are mainly outside Canada, it is a significant investor in Alberta's oil sands. It owns 65 percent of one sands project, with CNOOC as its minority partner, and has stakes in two other oil sands projects.

Some have expressed concern about a Chinese state-owned company gaining control of Nexen's Canadian assets, which include natural gas and shale gas properties.

Although Mr. Harper, the prime minister, does not usually tolerate criticism from within his party, some Conservative members of Parliament are among opponents of the Nexen deal. Rob Anders, a Conservative legislator who wants conditions placed on CNOOC, described China last month as being "a nonbenevolent actor and a strategic adversary."

But under Mr. Harper, and some predecessors, individual members of Parliament, even from his party, hold little sway.

Since American politics stalled plans to deliver more oil sands production to the United States through the Keystone XL pipeline, Mr. Harper has focused on China as Canada's next great energy market and courted Chinese fuel investment. That, analysts say, is likely to guide his thinking on CNOOC and Nexen more than what happens with Petronas.