Two trans-fat-free oil blends have passed the company's criteria, allowing Miami-based Burger King to begin the national launch. The company expects that every U.S. restaurant will be using trans-fat-free cooking oil by the end of 2008. If adequate supplies become available, the U.S. rollout of trans-fat-free oils could be completed "substantially sooner," the hamburger chain said.

"We are delighted by the outstanding consumer response to our new oil," Russ Klein, Burger King's president of global marketing, strategy and innovation, said in a statement. He said that in tests on over a dozen core items, consumers said food cooked in trans-fat-free oil tasted the same or better than products cooked in traditional oil.

The news comes as Burger King's rivals have switched or are in the process of switching to trans-fat-free oil. Burger King was hit with a lawsuit recently, filed by the nonprofit Center for Science in the Public Interest, which complained that the restaurant chain was lagging in the industry in ridding its menu of foods cooked in oil containing trans fat.

Trans fats can raise so-called bad cholesterol, doctors say, and may increase the risk of heart disease, stroke, diabetes and other health problems.

Other chains, including McDonald's Corp., Wendy's International Inc., Starbucks Corp., Yum Brands Inc., have either switched to healthier oils are in the process of replacing the oils they use.