The most polluting cruise ships operator was MSC Cruises – whose cruise ships emitted nearly as much SOx as all the passenger vehicles in Europe. Accounting for all of its subsidiaries, the Carnival group polluted the most. Many cruise operators like MSC are investing in fossil gas (LNG) as a cleaner alternative.

According to environmental reports leading into 2026, the world's largest cruise corporations, such as Carnival Corporation, Royal Caribbean Group, and Norwegian Cruise Line Holdings, are often cited as the most polluting due to the sheer scale of their fleets. For instance, Carnival Corporation's fleet has historically emitted more sulfur oxides than millions of cars combined. Specific brands like Princess Cruises and Norwegian Cruise Line have also faced scrutiny for high CO2​ emissions per nautical mile. While many lines are transitioning to Liquefied Natural Gas (LNG) to reduce sulfur and particulate matter, critics point to "methane slip"—the release of unburned methane—as a significant greenhouse gas concern. On the other end of the spectrum, smaller expedition lines like Hurtigruten are leading in efficiency by using hybrid-electric technology and shore power. The cruise industry as a whole is working toward net-zero emissions by 2050, but as of 2026, the largest "mega-ships" remain the primary contributors to maritime air pollution and wastewater challenges in port cities like Barcelona and Miami.