Emery's promise.(Emery Worldwide's guaranteed delivery program)

Emery Worldwide says its new guaranteed delivery program is about service, but experts say it's also a signal that freight carriers are looking for ways to boost their returns despite slowing demand.

"They are trying to get their rates up and their yield up, and they can't do it when fuel prices are so low," said David Campbell, an analyst with Virginia-based Scott & Stringfellow.

Emery launched the Guaranteed Service Program in the United States, Canada and Puerto Rico last month, expanding on its other guaranteed services by offering guarantees without pre-booking requirements. Emery says it will try to steer existing customers to the new service, which …