including the 11 members of the aforementioned Vista class, and all at or greater. The only comparable ocean liner to be completed in recent years has been Cunard Line's in 2004. Following the retirement of her running mate Queen Elizabeth 2 in November 2008, Queen Mary 2 is the only liner operating on transatlantic routes, though she also sees significant service on cruise routes. Queen Mary 2 was for a time the largest passenger ship before being surpassed by Royal Caribbean International's vessels in 2006. The Freedom-class ships were in turn overtaken by RCI's own vessels which entered service in 2009 and 2010. A distinctive feature of the Oasis-class ships is the split, atrium structure, made possible by the hull's extraordinary width, with the 6-deck high Central Park and Boardwalk outdoor areas running down the middle of the ship and verandas on all decks. In two short decades (1988–2009), the largest class cruise ships have grown a third longer (), almost doubled their widths (), doubled the total passengers (2,744 to 5,400), and tripled in volume (73,000 to 225,000 GT). Also, the "megaships" went from a single deck with verandas to all decks with verandas. Cruise lines Operators of cruise ships are known as cruise lines, which are companies that sell cruises to the public. Cruise lines have a dual character; they are partly in the transportation business, and partly in the leisure entertainment business, a duality that carries down into the ships themselves, which have both a crew headed by the ship's captain, and a hospitality staff headed by the equivalent of a hotel manager. Among cruise lines, some are direct descendants of the traditional passenger shipping lines (such as Cunard), while others were founded from the 1960s specifically for cruising. Historically, the cruise ship business has been volatile. The ships are large capital investments with high operating costs. A persistent decrease in bookings can put a company in financial jeopardy. Cruise lines have sold, renovated, or renamed their ships to keep up with travel trends. Cruise lines operate their ships almost constantly. If the maintenance is unscheduled, it can result, potentially, in thousands of dissatisfied customers. A wave of failures and consolidations in the 1990s led to many cruise lines being bought by much larger holding companies and continue to operate as "brands" or subsidiaries of the holding company. Brands continue to be maintained partly because of the