Ford is hoping to expand its hybrid range beyond that of its current Escape Hybrid and Mercury Mariner models but is being held back by engineering problems surrounding the development of rechargeable electric cars. The head of its hybrid and sustainable vehicle programs, Nancy Gioia, has revealed that Ford has "more full hybrids coming,” reports Reuters.

Ford was the first of America’s Big Three to release a hybrid when it launched the original Escape Hybrid back in 2004, but has not progressed much in the enviro stakes since and was in fact criticized for a lack of clean powertrains.

Though sales of Toyota’s Prius in the US has almost doubled in the first five months of the year, compared with the same period last year, sales of Ford's Escape and Mariner have only increased by 8%.

Ford’s goal now is to develop a reliable plug-in hybrid that would be capable of running on electrical power alone for short trips and could be fully charged by a household power outlet. Gioia revealed that Ford is stuck on the development of suitable battery technology, in stark contrast to the claims of its main rival GM, which expects to release its own plug-in vehicle by the end of the decade.