Royal Caribbean's Allure of the Seas departs for the Caribbean earlier this month from Port Everglades in Fort Lauderdale, Fla. The ship — which has 2,706 rooms, 16 decks, 22 restaurants, 20 bars, 10 hot tubs and many other amenities — can accommodate nearly 6,300 passengers and 2,394 crew members. Such massive ships are worrying safety experts and lawmakers.

One of the largest cruise ships in 1985 was the 46,000-ton Carnival Holiday. Ten years ago, the biggest, the Queen Mary 2, was three times as large. Today’s record holders are two 225,000-ton ships whose displacement, a measure of a ship’s weight, is about the same as that of a Nimitz-class aircraft carrier.

Cruise ships keep getting bigger, and more popular. The Cruise Lines International Association said that last year its North American cruise line members carried about 17 million passengers, up from 7 million in 2000. But the expansion in ship size is worrying safety experts, lawmakers and regulators, who are pushing for more accountability, saying the supersize craze is fraught with potential peril for passengers and crew.

“Cruise ships operate in a void from the standpoint of oversight and enforcement,” said James Hall, a safety management consultant and the chairman of the National Transportation Safety Board between 1994 and 2001. “The industry has been very fortunate until now.”

The perils were most visible last year when the Costa Concordia, owned by the Carnival Corp., which is based in Miami, capsized off Italy. The accident killed 32 people and revealed fatal lapses in safety and emergency procedures.

In February, a fire crippled the Carnival Triumph, stranding thousands without power for four days in the Gulf of Mexico until the ship was towed to shore. Another blaze forced Royal Caribbean’s Grandeur of the Seas to a port in the Bahamas in May. Pictures showed the ship’s stern blackened by flames and smoke.

Although most have not resulted in any casualties, the string of accidents and fires has heightened concerns about the ability of megaships to handle emergencies or large-scale evacuations at sea. Sen. John D. Rockefeller IV, D-W.Va., introduced legislation this summer that would strengthen federal oversight of cruise lines’ safety procedures and consumer protections.

Cruise operators point out that bigger ships have more fire safety equipment, and contend they are safer. After a fire aboard the Carnival Splendor three years ago, Carnival adopted new training procedures and added safety features that it says helped with the rapid detection and suppression of the fire on the Triumph.

After the Triumph fire, Carnival also announced it would spend $700 million to improve its safety operations, including $300 million on its fleet of 24 Carnival Cruise Lines ships. The company is the largest cruise operator, owning about half of worldwide cruise ships.

“We have over time improved the safety of our vessels by better training and better technology and learning from incidents that have happened over the years,” said Mark Jackson, Carnival’s vice president for technical operations, who joined the company in January after 24 years with the Coast Guard.

Some experts doubt that ships can grow much larger than the current behemoths, marvels of naval engineering that combine cutting-edge technology and entertainment. Today’s biggest ship, Royal Caribbean’s Allure of the Seas, has 2,706 rooms, 16 decks, 22 restaurants, 20 bars and 10 hot tubs, as well as a shopping mall, a casino, a water park, a half-mile track, a zip line, mini golf and Broadway-style live shows. It can accommodate nearly 6,300 passengers and 2,394 crew members — the equivalent of a small town towering over the clear blue waters of the Caribbean Sea. It measures 1,188 feet long. Its sister ship, the Oasis of the Seas, is 2 inches shorter.

Experts point out that larger ships have larger challenges. For instance, they have fewer options in an emergency, said Michael Bruno, dean of the engineering school at the Stevens Institute of Technology in Hoboken, N.J., and former chairman of the National Research Council’s Marine Board.

“Given the size of today’s ships, any problem immediately becomes a very big problem,” he said. “I sometimes worry about the options that are available.”