McDonald's is finally switching to a new trans-fat-free oil. The healthier oil will be used for cooking McDonald's famous french fries after years of testing, the fast-food chain said Monday.

However, McDonald's is still not saying when the new zero-trans fat oil oil will be used in all 13,700 U.S. restaurants. McDonald's and other fast-food chains face a July 1, 2007 deadline to comply with an ordinance passed by New York City to ban all restaurants from using artificial trans fats.

McDonald's spokesman Walt Riker said the oil is currently in more than 1,200 U.S. restaurants after extensive testing, but declined to provide details on timing or locations.

"We can confirm that we've got the right oil. We're phasing it in," Ricker said, adding that the new oil is canola-based and includes corn and soy oils.

Addressing long-held concerns that changing the oil could jeopardize the popular taste of its fries, he said: "We're very confident in our test and taste results. ... We're very confident in what we're hearing back from our customers."

The Chicago Tribune, which first reported McDonald's decision on a new oil Sunday, said the company has tested 18 varieties of oil in more than 50 blends during the last seven years.

McDonald's had been under pressure for moving more slowly to rid its oil of the artery-clogging trans fats. Public health advocates criticized McDonald's fries cooked on trans fats as nutritionally "disastrous."

After the news about the healthier oil shares in McDonald's rose 35 cents to $43.28 in afternoon trading on the New York Stock Exchange.