Seven months after its debut, Royal Caribbean's much-ballyhooed Oasis of the Seas continues to command a large premium vs. the line's other vessels.

Wall Street's Majestic Research says in a new report the world's largest ship has been selling for roughly 41% more, on average, than the rest of the Royal Caribbean fleet for the current quarter. The least expensive interior cabins are selling for 69% more, on average.

When it first came out in December 2009, interior cabins on the 5,400-passenger vessel sold for a stratospheric 142% premium to other Royal Caribbean ships, according to an earlier Majestic Research report. The premium for interior cabins dropped to 112% in the first quarter of 2010 and 74% in the second quarter, according to the firm.

"We expect the ship will continue to generate strong premiums throughout most of 2010, although premiums appear to be leveling off sequentially," writes Majestic Research's Matthew Jacob.

Jacob says he expects Oasis will continue to have the largest premium of any of Royal Caribbean ships until the December introduction of its sister vessel, Allure of the Seas.

The bad news for Royal Caribbean, according to Jacob: While Oasis continues selling for a high mark-up, the ship appears to be cannibalizing the rest of the fleet.

"Most telling is the impact to (Royal Caribbean's) Freedom class and (sister company Celebrity Cruises') Solstice class ships, which have seen their premiums decline significantly since the launch of Oasis," says Jacob.

Jacob says Freedom class ships have seen their premium for interior cabins
versus the rest of the Royal Caribbean fleet shrink to 4% during the current quarter from 27% during the same quarter last year (the last full quarter prior to the launch of Oasis). Celebrity's Solstice class ships have seen their premiums decline to 22% during the current quarter from 68% during the same quarter a year ago, he says.