Some 145,000 passengers and 43,000 cars are booked to cross the Irish Sea with Stena Line over Christmas.
The numbers refer to sailings back and forth across the Irish Sea between December 16 and January 3.
With 224 weekly crossings across the company's five routes between Ireland and Britain, there is still very limited availability for anyone who hasn't booked yet.
Stena's Diane Poole said December 21-23 is the busiest period on the ferries.
"Our crossings from January 2-4 are also particularly busy, as people return home after the Christmas holidays.
"However, given the size of our fleet and choice of routes, we still have some very limited availability for anyone planning a last-minute trip home, but you'd really need to be booking as soon as possible to avoid disappointment. We have no sailings on Christmas Day on any of our routes."