Faced with escalating fuel costs and increasingly stringent environmental regulations, the state ferry system hopes to convert at least a quarter of its fleet to a new fuel source.

The goal is to convert six ferries to run on liquefied natural gas by 2015, according to David Moseley, head of the ferry system.

The ferry system has been studying liquefied natural gas (LNG) for about two years, Moseley said, adding that it is expected to remain significantly cheaper than the diesel fuel that ferries currently use. Moseley said it also produces fewer greenhouse gas emissions.

WSF recently got preliminary approval from the U.S. Coast Guard to retrofit the six Issaquah class ferries. It now will develop more specific plans, which it will present to the Coast Guard as well as the state Legislature for approval as early as this winter. It’s also searching for a private investor, perhaps a natural gas supplier, to help finance the multi-million dollar project.