McDonald's Corp. (MCD) Chief Executive Jim Skinner said Wednesday the fast-food chain is making "very good progress" toward developing a healthier oil for french fries cooked in its U.S. restaurants but still would not give a timetable for when a switch will be made.

Four years after the company first pledged to significantly reduce the trans fats levels in its signature fries, Skinner told an investor conference that the company continues to work hard on a new oil.

He said that if New York passes a proposed ordinance making it the first U.S. city to ban eateries from serving food containing trans fat, McDonald's will be ready to comply.

"We're making very good progress on this, and yet we're taking the approach that we're not going to announce, and predict timing on it. But we will get there," Skinner told analysts at the New York conference. "It's just taking a little bit of time because as we move forward we don't want to jeopardize the iconic nature of the french fry, which as you know is so very important to our brand."

McDonald's said in September 2002 that it would introduce a new oil halving the amount of trans fats, but it delayed the plan indefinitely a few months later amid concerns about changing the taste of the fries.

The Oak Brook, Ill.-based company has been quietly testing new blends in select U.S. restaurants but has avoided making a full commitment like some of its fast-food competitors. Wendy's International Inc. switched to a zero-trans fat oil in August and Yum Brands Inc.'s KFC said Oct. 30 that it will stop using oil with trans fats by April.

Skinner also said McDonald's is experiencing its strongest business results in 30 years, including 42 consecutive months of increases in worldwide comparable sales, or those from restaurants open more than a year.

Longer operating hours, cashless payment options and new products all have combined to fuel a surge in the company's U.S. business, its largest market, since 2002.

Chief Financial Officer Matt Paull said the new chicken Snack Wrap sandwich, introduced in U.S. restaurants in late July, is "one of our most successful launches ever" and has attracted new customers.

Paull also said the company expects to return at least $10 billion to shareholders from 2006 through 2008, or more than double the $4.3 billion in cash returned to shareholders from 2003-05.

Shares in the company fell 4 cents to $41.23 in midday trading on the New York Stock Exchange.