BP PLC and Husky Energy Inc., Canada's No. 5 oil-and-gas producer, said Wednesday they would invest $5.5 billion (¤3.7 billion) over the next seven years in the third large cross-border deal to tie up Canadian oil sands output with U.S. refining, according to AP. Mimicking last year's $10.7 billion deal between ConocoPhillips and Canada's biggest producer, EnCana Corp., the companies will exchange stakes in Husky's Sunrise oil sands venture in Alberta and BP's Toledo, Ohio, refinery through a pair of joint ventures. The partnership is effective Jan. 1, 2008, and following regulatory approval, the deal is expected to close in the first quarter. Canada is the biggest crude-oil exporter to the United States, accounting for nearly a fifth of its southern neighbor's imports, and there's a deepening of already strong ties between the two countries. ConocoPhillips and EnCana kicked off the trend in October 2006, while Marathon Oil Corp. recently closed its takeover of Western Oil Sands Inc., a minority partner in the vast Athabasca oil sands project led by Royal Dutch Shell PLC. The announcement coincides with the Organization of Petroleum Exporting Countries' decision earlier Wednesday to maintain current crude output levels.