Most large cruise ships run on diesel engines, but newer ships are switching to liquefied natural gas

A cruise ship's power comes from one of three sources: heavy fuel oil burned in diesel engines, liquefied natural gas (LNG) burned in dual-fuel engines, or a combination of both. The engine drives a propeller or multiple propellers that move the ship through water. That same engine also powers a generator that produces electricity for the ship's lights, air conditioning, kitchens, and cabins. Older ships built before 2015 almost always use heavy fuel oil. Newer ships, particularly those built after 2020, increasingly use LNG because it produces less sulfur and nitrogen pollution.

The choice of fuel affects operating cost, environmental impact, and how often the ship needs to refuel. A large cruise ship burns between 50 and 300 tons of fuel per day depending on size, speed, and sea conditions. That fuel cost is one reason cruise lines are investing in LNG technology, even though LNG-powered ships cost more to build.

Key Takeaways

  • Heavy fuel oil powers most cruise ships built before 2015, while newer ships increasingly use liquefied natural gas or a combination of both.
  • The main engine drives the propeller and also powers a generator that supplies electricity to the entire ship.
  • Cruise ships burn 50 to 300 tons of fuel daily depending on size and speed, making fuel choice a major operating expense.
  • LNG produces less air pollution than heavy fuel oil but requires specialized storage tanks and refueling infrastructure that does not exist in all ports.
  • Backup diesel generators run when the main engine is off or during emergencies to keep lights, navigation, and safety systems working.

How diesel engines power the ship and its systems

A cruise ship's main diesel engine is enormous—some are as tall as a three-story building and weigh over 2,000 tons. The engine burns heavy fuel oil (also called bunker fuel), which is thicker and cheaper than the diesel you put in a car. This fuel is heated before it enters the engine so it flows properly. The engine's pistons compress the fuel and ignite it, creating the power that turns the propeller shaft.

The same engine that moves the ship also drives an electrical generator. This generator produces the power for everything else on board: cabin lights, air conditioning, refrigeration, elevators, and the galley (ship's kitchen). On a large ship, the generator produces enough electricity to power a small town. If the main engine shuts down for maintenance or repair, backup diesel generators automatically start to keep essential systems running.

Heavy fuel oil is cheap and energy-dense, which is why it remains the standard for older ships. The downside is that it produces sulfur dioxide and nitrogen oxides when burned, which contribute to air pollution. Ships operating in European waters and near major ports must use lower-sulfur fuel or install scrubbers—devices that clean the exhaust—to meet environmental regulations.

Liquefied natural gas as an alternative fuel

Liquefied natural gas (LNG) is natural gas cooled to minus 162 degrees Celsius, which turns it into a liquid that takes up far less space than gas. When LNG is stored in a ship's fuel tank and warmed slightly, it becomes gas again and burns in a dual-fuel engine. The engine can switch between LNG and heavy fuel oil depending on what fuel is available at each port.

LNG produces roughly 25 percent less carbon dioxide than heavy fuel oil and almost no sulfur dioxide. It also produces fewer nitrogen oxides. For cruise lines operating in regions with strict environmental rules—particularly Northern Europe and the Baltic Sea—LNG reduces the cost of compliance. Ships like Royal Caribbean's Icon and Disney Cruise Line's Disney Wish use LNG engines.

The challenge is infrastructure. LNG refueling stations exist in only a handful of ports worldwide, mostly in Northern Europe and a few in Asia. A ship powered only by LNG cannot operate on routes where LNG is not available. This is why most LNG-powered ships are dual-fuel: they can burn LNG when it is available and switch to heavy fuel oil when it is not. Building an LNG-powered ship costs 10 to 15 percent more than building a comparable diesel ship, which is why older vessels have not been retrofitted.

Backup power and emergency systems

Every cruise ship carries backup diesel generators separate from the main engine. These generators are smaller and run on marine diesel fuel. They start automatically if the main engine fails or shuts down. On a ship at sea, losing electrical power is dangerous—navigation systems, communication equipment, and safety lighting all depend on electricity. The backup generators may support these critical systems stay online.

Backup generators also run during port calls when the main engine is off. Instead of idling the massive main engine just to produce electricity while docked, the ship switches to smaller, more efficient backup generators. This saves fuel and reduces emissions in port areas where air quality matters most to nearby communities.

Ships also carry battery systems on some newer vessels, though these are not yet large enough to power an entire ship. Batteries are used to smooth out power demand and reduce the load on generators during peak usage times, similar to how a home battery system works with solar panels.

How ship propulsion systems have changed

For most of the 20th century, cruise ships used steam turbines powered by oil-fired boilers. Steam turbines were reliable but inefficient—they wasted a lot of energy as heat. In the 1980s and 1990s, cruise lines switched to diesel engines, which are more fuel-efficient and require less maintenance. Diesel engines became the industry standard and remain so today.

The shift to LNG is the next major change. The first LNG-powered cruise ship, AIDAnova, entered service in 2018. Since then, several major cruise lines have ordered LNG ships. However, the transition is slow because LNG infrastructure is limited and building LNG ships is expensive. Most cruise ships operating today still burn heavy fuel oil, and that will remain true for at least another decade.

Future developments may include hydrogen fuel cells or advanced battery systems, but these technologies are still in early testing phases for large ships. The size and weight of batteries needed to power a cruise ship for a week at sea make them impractical with current technology.

Fuel consumption and operating costs

A large cruise ship carrying 5,000 passengers and crew burns between 50 and 300 tons of fuel per day. The exact amount depends on the ship's size, speed, and sea conditions. Rough seas require more power to maintain speed, so fuel consumption increases. Ships also burn more fuel when traveling at higher speeds. Most cruise lines operate ships at moderate speeds to balance fuel cost against schedule.

Fuel is typically the second-largest operating expense for a cruise line, after labor. A single large ship can spend $20,000 to $50,000 per day on fuel, depending on fuel prices and consumption. Over a year, that adds up to millions of dollars. This is why cruise lines invest in more efficient engines and why the shift to LNG is economically attractive—LNG often costs less per unit of energy than heavy fuel oil, even accounting for the higher cost of building an LNG ship.

Fuel prices fluctuate based on global oil markets. When oil prices rise, cruise lines either absorb the cost or pass it to customers through fuel surcharges added to ticket prices. Some cruise lines hedge fuel costs by locking in prices months in advance, similar to how airlines manage jet fuel expenses.

Environmental regulations and emissions standards

International maritime regulations, set by the International Maritime Organization (IMO), limit the sulfur content of ship fuel. Ships operating in designated emission control areas—including waters near Europe, North America, and parts of Asia—must use fuel with sulfur content below 0.1 percent or install scrubbers that remove sulfur from exhaust. Ships operating in other waters can use higher-sulfur fuel, which is cheaper.

The IMO also requires ships to report their fuel consumption and carbon emissions. Starting in 2024, ships must meet minimum energy efficiency standards. Ships that do not meet these standards must reduce fuel consumption or face penalties. These regulations push cruise lines toward more efficient engines and cleaner fuels like LNG.

Individual countries and regions add their own rules. California requires ships to use lower-sulfur fuel within 24 nautical miles of the coast. The European Union is considering a carbon tax on shipping. These patchwork regulations create complexity for cruise lines operating global routes, but they also drive investment in cleaner technology.

Frequently Asked Questions

Why do cruise ships burn such dirty fuel?

Heavy fuel oil is cheap and energy-dense, making it economical for ships that burn massive quantities daily. International regulations allow it in most waters. Ships operating near populated coasts must use cleaner fuel or install scrubbers. The shift to LNG is happening, but it requires new infrastructure and higher upfront costs.

Can cruise ships run on electricity from shore power?

Yes. When a ship is docked, it can plug into shore power (called cold ironing) to run its systems instead of running generators. This reduces emissions in port. However, not all ports have shore power infrastructure, and retrofitting older ships to use it is expensive. Most cruise ships still rely on onboard generators while docked.

How long can a cruise ship run on fuel?

A large cruise ship carries enough fuel for roughly 12 to 14 days of continuous operation at normal cruising speed. Most cruise itineraries are 7 to 10 days, so ships refuel at ports along the route. Ships on longer voyages refuel more frequently. Fuel capacity varies by ship size and design.

Do cruise ships have solar panels or wind power?

A few newer ships have small solar panel arrays that supplement onboard power, but they produce only a tiny fraction of the ship's total electricity needs. The surface area available on a ship is small compared to its power demand. Wind power is not practical for cruise ships because the engines must run continuously regardless of weather. Solar and wind remain experimental additions rather than primary power sources.

What happens if a cruise ship runs out of fuel at sea?

Modern ships have fuel management systems that alert the crew well before fuel runs critically low. Ships are designed to reach the next port with fuel reserves. If a ship truly ran out of fuel, it would lose propulsion and electrical power, which is why this is treated as a serious emergency. Ships carry backup fuel supplies and can request fuel transfers from supply vessels if needed.