Road Equivalent Tariff (RET), which links the cost of fares to travelling an equivalent distance on land, is to be rolled out to all of the remaining ferry routes in the Clyde and Hebrides Ferry Services (CHFS) network from October, next year.
It will see significant discounts offered on 14 routes for passengers, cars, small commercial vehicles and coaches. RET was first introduced on Western Isles, Coll and Tiree services in 2008 before being expanded to Islay, Colonsay and Gigha in 2012. It will be introduced for Arran this autumn.
The newly added routes, which will offer RET from October 2015, include Barra to Eriskay, Oban to Craignure, Wemyss Bay to Rothesay and Largs to Cumbrae.
Transport Minister Keith Brown said: "We have already seen the positive impact of RET on other ferry routes around Scotland - this further roll out is expected to bring similar economic and tourism benefits.
"We would expect a reduction in fares to lead to an increase in demand on these services, particularly during the summer timetable. We will therefore work with members of the affected communities to find ways of managing this demand."
However, Orkney Liberal Democrat MSP, Liam McArthur, said it was "unfair and unacceptable" that some islands benefited from RET and others, such as the Northern Isles, did not.
"Reducing the cost of getting to and from our islands can deliver enormous economic and social benefits to these communities," he said. "It should be a key commitment for any government. However it must be done on the basis of fairness to all."