The company predicts that 900,000 people a year could use the 20-minute crossing between Kirkcaldy and Leith within four years.
It is seeking £3.3 million in launch funding from the Scottish Government and the South East Scotland Transport Partnership. It hopes that the service will be operational by summer 2009.
More than 32,000 passengers used the service during the two-week trial in July. "The trial proves that there is huge support for this project from both sides of the Forth and it is crucial that we maintain the momentum," said Stagecoach chief executive Brian Souter.