AT&T Inc will spend $565 million within 10 years to replace or buy about 15,000 vehicles in its corporate fleet with cars and other vehicles that run on alternative fuels, the company said on Wednesday.

The U.S. telecommunications giant said the investment would be the biggest of its kind by a U.S. company and struggling Ford Motor Co would be a key beneficiary.

AT&T Chief Executive Officer Randall Stephenson told the Economic Club of Washington that fleet modernization would significantly lower fuel costs.

The company said it will buy about 8,000 vehicles that run on compressed natural gas over five years -- to be built by Ford Motor Co.

Natural gas is cheaper, cleaner and we have plenty of it here domestically, Stephenson said in comments prepared for delivery to the meeting.

AT&T also plans to replace 7,100 other vehicles with hybrids and other advanced technology power systems over 10 years.