Most cruise ships burn heavy fuel oil (HFO), a thick, tar-like residual product left over after crude oil is refined into lighter fuels like gasoline and diesel. A growing number of newer ships run on liquefied natural gas (LNG), and the industry is beginning to experiment with greener alternatives like methanol and biofuels. The fuel choice depends on the ship’s age, its engines, and the environmental regulations in the waters it sails through.
Heavy Fuel Oil: The Industry Standard
Heavy fuel oil has been the default cruise ship fuel for decades, and it still powers the majority of the global fleet. It’s essentially the bottom-of-the-barrel residue from oil refining: dense, high in sulfur, and so thick at room temperature that it has to be heated before engines can burn it. HFO is popular for one simple reason: it’s cheap. Because it’s a byproduct that other industries don’t want, it costs significantly less per ton than cleaner alternatives.
The downside is environmental. HFO contains high levels of sulfur, nitrogen, and heavy metals. When burned, it produces sulfur oxides, nitrogen oxides, and fine particulate matter that contribute to air pollution and acid rain. Before 2020, ships could burn fuel with up to 3.5% sulfur content on the open ocean. That’s 3,500 times the sulfur limit for car diesel in many countries.
How Regulations Changed the Fuel Mix
In January 2020, the International Maritime Organization (IMO) imposed a global cap limiting sulfur in ship fuel to 0.50% by mass, down from 3.5%. In designated Emission Control Areas, which include much of the North American and Northern European coastlines, the limit is even stricter at 0.10%.
Cruise lines adapted to these rules in three main ways. Some switched to lower-sulfur fuels like marine gas oil (MGO), a lighter, cleaner distillate fuel similar to diesel. Others installed exhaust gas cleaning systems, commonly called scrubbers, which let them keep burning cheaper high-sulfur HFO while stripping sulfur oxides out of the exhaust. A smaller number of new ships were built to run on LNG, which produces almost no sulfur emissions at all.
How Scrubbers Work
Open-loop scrubbers spray seawater through the exhaust stream. The natural alkalinity of the seawater neutralizes sulfur oxides, and the wash water is then diluted and discharged back into the ocean. Closed-loop systems recirculate freshwater treated with a chemical solution to neutralize the sulfur, minimizing what gets released overboard. Many newer installations are hybrid systems that can switch between the two modes depending on local port regulations, since some harbors have banned open-loop scrubber discharge over concerns about water quality.
Marine Gas Oil and Marine Diesel Oil
Marine gas oil (MGO) and marine diesel oil (MDO) are the cleaner liquid fuel options. Both are distillate fuels, meaning they come from the lighter, more refined fractions of crude oil rather than the heavy residue. MGO is the cleanest of the two, with lower density and fewer impurities. MDO sits between MGO and HFO, sometimes containing a small blend of heavier components.
These fuels are what cruise ships typically switch to when entering Emission Control Areas or ports with strict air quality rules. They burn more cleanly, produce less particulate matter, and meet the 0.10% sulfur limit without scrubbers. The trade-off is cost: distillate fuels are considerably more expensive than HFO, which is why many operators prefer scrubbers for open-ocean sailing.
Liquefied Natural Gas: The Cleaner Alternative
LNG is the biggest shift in cruise ship fuel in the past decade. Natural gas is cooled to minus 162°C (minus 260°F), which shrinks it to about 1/600th of its gaseous volume, making it practical to store on board. Several major cruise lines now operate LNG-powered ships, and most large newbuilds are being designed with LNG capability.
The emissions benefits are real. A sea trial study measuring on-board exhaust found that switching from marine gas oil to LNG at high engine loads reduced fine particulate emissions by a factor of roughly 136. CO2-equivalent emissions dropped by about 18% compared to MGO at 75% engine load. LNG also produces virtually no sulfur oxides, eliminating the need for scrubbers entirely.
LNG isn’t a perfect solution, though. One concern is methane slip, where small amounts of unburned methane escape through the engine exhaust. Methane is a far more potent greenhouse gas than CO2 over shorter time horizons, which can offset some of the carbon benefits depending on engine design and load conditions. The infrastructure for LNG bunkering (refueling) is also still limited to certain ports, which restricts route flexibility.
How Much Fuel a Cruise Ship Burns
A large cruise ship can consume up to 250 tons of fuel per day. To put that in perspective, that’s roughly equivalent to 80,000 gallons of regular gasoline, far more than the average person would burn driving cars over an entire lifetime. Fuel consumption varies widely depending on the ship’s size, speed, passenger count, and weather conditions. Smaller expedition ships might use a fraction of that, while the largest mega-ships with 6,000 or more passengers burn through fuel at the upper end of the range.
For passengers, the carbon math works out to roughly 317 grams of CO2 per passenger per nautical mile on a typical large ship burning conventional fuel. An analysis by the International Council on Clean Transportation estimated that a 2,000-nautical-mile Alaska cruise generates about 1.5 metric tons of greenhouse gas emissions per passenger when the ship runs on HFO, comparable to the emissions from a round-trip flight between San Francisco and Seattle plus weeks of daily driving.
Shore Power at Port
When a cruise ship is docked, it still needs electricity for lighting, air conditioning, kitchens, and entertainment. Traditionally, ships kept their diesel generators running in port, pumping exhaust into the surrounding neighborhood. Shore power, also called cold ironing, lets a ship plug into the local electrical grid and shut down its generators entirely.
The technology works, and it dramatically cuts port-side air pollution. The barrier is infrastructure: building shore power connections requires substantial investment from both ports and cruise lines, and the ship’s electrical systems have to be compatible with the local grid. Adoption is expanding, particularly in Europe and along the U.S. West Coast, but it’s far from universal. Many ports in the Caribbean, Mediterranean, and Asia still lack the necessary hookups.
Green Methanol, Biofuels, and What’s Next
The cruise industry has committed to reaching net-zero carbon emissions by mid-century, and LNG alone won’t get there. Several lines are now exploring fuels that could close the gap. Green methanol, produced from renewable sources like biomass or captured CO2 combined with green hydrogen, is one of the leading candidates. Princess Cruises is conducting a feasibility study to run four ships on green methanol for full Alaska itineraries by 2032, and other lines are investigating similar pathways.
Biofuels are attractive because they work as “drop-in” replacements for existing fuels, meaning ships don’t need new engines or major retrofits. A ship designed to burn marine diesel can often switch to biodiesel blends with minimal modification. The challenge is supply. There simply isn’t enough sustainable biofuel feedstock available to power the global cruise fleet, and the cruise industry competes for that supply with aviation, trucking, and other sectors all trying to decarbonize at the same time.
Hydrogen fuel cells and battery-hybrid systems are also under development, but they face significant energy density challenges. Hydrogen takes up far more space than conventional fuel for the same amount of energy, which is a serious constraint on ships that need to cross oceans without refueling. For now, these technologies are more likely to appear in short-range ferries and port operations than on oceangoing cruise ships.