Viking Cruises has upped its order for new Viking Longships from 12 to 14 for the 2014 season.
It said the decision comes after "record levels of consumer interest in river cruising".
The increase will bring the total number of new ships launched in the past three years to 30, the most rapid fleet expansion programme the cruise industry has ever seen.
River cruising has grown at an average annual rate of about 9%, Viking said, while its own business has grown 22%.
Even with 10 new ships sailing its European routes in 2013, the line had occupancy rates of 90% in the spring and summer.
By Cheryl Rosen, TravelMole US
