THE Isle of Wight faces cross-Solent fares hikes and possible cuts in services when new fuel rules come into effect in 2015.
Wightlink warned the ferry industry predicted both journey cuts and higher fares caused by increased fuel bills.
Diesel will cost more when the 2015 international agreement insists all ferries use higher-grade fuels, which produce much lower emissions.
A Wightlink spokesman said: "The most likely outcome for Wightlink will be journey cuts in an attempt to keep fare increases as low as possible, while at the same time maintaining a credible, effective service, which we know is vital to the economic and social well-being of the Island.
"Of course, the impending ruling will result in extra costs to provide the service but, as yet, we are not in a position to determine the exact details.
"We will be taking everything into account before making a decision, which will reflect our usual policy of ensuring the impact on our customers is as small as possible."
Even though Red Funnel is already complying with the international agreement before it comes into effect, it warned its fares could still rise.
Sales and marketing director Jonathan Green said: "Red Funnel’s Red Jet and vehicle ferry fleet already uses diesel with a sulphur content of just 0.1 per cent.
"Although more expensive than low-grade fuel, it does mean the company is in compliance with the 2015 legislation.
"The only concern is whether increased demand from the shipping sector and a lack of refining capacity culminates in higher prices for diesel at the pumps."