Ship with LNG tank

LNG as fuel for ships: expert answers to 17 important questions

LNG is a cost-effective fuel that reduces greenhouse gas emissions and other harmful pollutants. Want to know more? Find out in these 17 expert answers.

With emissions regulations getting ever stricter, many ship owners are turning to alternative fuels to power their vessels. Liquified natural gas (LNG) is proving a popular choice – and for good reason. Want to know more about LNG as fuel? Get an expert overview in 17 important questions.

Your choice of fuel affects both your profitability and your vessel’s environmental compliance. Liquefied natural gas (LNG) is a safe and cost-effective fuel that reduces greenhouse gas emissions and other harmful pollutants. LNG is playing a key role as a transition fuel and is widely seen as the first step towards decarbonising the maritime industry.

Switching to LNG as fuel for ship propulsion requires investment but can save you fuel costs, increase your profitability and reduce compliance risks. The expert answers to these 17 questions will tell you what you need to know about LNG as an alternative fuel for shipping.


1. What is LNG?

LNG is natural gas that has been cooled to -162°C (-260°F), turning it into a clear, odourless liquid that is easy to ship and store. LNG is typically 85–95% methane, which contains less carbon than other forms of fossil fuels. It is a compact, efficient form of energy that is ideal for ship propulsion.


2. What is LNG used for?

LNG is primarily used as a clean-burning energy source. It is used for electricity generation, heating, cooking, and as a transportation fuel. LNG is also used as a raw material for products like fertilisers and plastics.

In the shipping industry, LNG as fuel is used for ship propulsion, auxiliary power generation and other onboard energy needs. LNG as an alternative fuel for shipping has gained wide popularity due to its clean-burning properties and potential to help meet stricter emissions regulations.

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3. What are the sources of LNG as fuel for ships? What is bioLNG?

LNG as fuel for ships is produced from natural gas extracted from underground reserves, including both onshore and offshore gas fields.

BioLNG is LNG produced from biogas, which is generated from organic waste like food scraps, agricultural waste, manure and sewage sludge. BioLNG is considered a renewable fuel and can further reduce the carbon footprint of ships using LNG fuel systems.


4. Is LNG just methane?

LNG is primarily methane (typically 85–95%), but it also contains small amounts of ethane, propane and other hydrocarbons. LNG can also contain trace amounts of nitrogen and carbon dioxide. The exact composition of LNG may vary depending on the source of the natural gas and the liquefaction process used.


5. LNG fuel vs. fuel oil: is LNG better than diesel?

Compared to diesel fuel oil, LNG offers several advantages. LNG produces significantly lower emissions when burned, including:

  • 20–30% less CO2 
  • 15-25% less total GHG
  • 90% less NOx 
  • 99% less SOx 
  • Almost no particulate matter (PM) 

LNG engines are also quieter. 

However, LNG has a lower energy density than diesel, so using LNG as an alternative fuel for shipping will require more fuel and therefore larger fuel tanks to achieve the same range.


6. What are the advantages and disadvantages of LNG fuel?

The key advantages of LNG as fuel include reduced emissions and cost competitiveness. There is also an established and continuously growing global network of LNG bunkering facilities.

The disadvantages of using LNG as fuel for ships include the need for specialised equipment and training and the potential for methane slip.

Methane slip is when unburned methane, a potent greenhouse gas, escapes into the atmosphere. Modern dual-fuel engines will minimise this issue. Depending on engine type and load, you can reduce methane slip by up to 65% by upgrading your ship’s existing engines. Over the last 30 years, Wärtsilä has reduced the methane slip from its engines by around 90%.

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7. Is LNG environmentally friendly?

LNG is cleaner burning than traditional marine fuels, but it is still a fossil fuel. BioLNG, which is LNG produced from organic waste or biomass, can be considered a more sustainable alternative to fossil-based LNG as it has a lower carbon footprint. However, the production and combustion of bioLNG still emit some greenhouse gases. LNG can be seen as a bridging fuel in the transition to alternative fuels like methanol and ammonia, which aren’t yet widely available at scale.


8. Is LNG a future fuel?

LNG both is and isn’t a future fuel. It enables lower greenhouse gas emissions and reduces other harmful air pollutants compared to fuel oil, but it is still a fossil fuel. Sustainable future fuels are crucial for maritime decarbonisation, but the current cost, limited availability and insufficient infrastructure are challenging for operators. This gives LNG an important role to play in the shipping industry’s transition to a zero-carbon future.

As more ports develop LNG bunkering infrastructure and more ships are built with LNG fuel systems, the use of LNG as an alternative fuel for shipping is expected to increase. LNG is considered a stepping stone on the path to decarbonisation as the industry moves closer to using true future fuels such as methanol and ammonia.

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9. What are the problems of LNG?

There are two main problems with LNG as fuel. Firstly, specialised equipment and training are needed to handle LNG safely. Secondly, LNG is predominantly methane and when burned as fuel unburned methane can escape into the atmosphere. This is known as methane slip and can offset LNG’s environmental benefits because methane is a potent greenhouse gas.

Modern dual-fuel engines can minimise methane slip – in fact, Wärtsilä has reduced methane slip from ship engines by around 90% over the last three decades through engine upgrades and ongoing research and development. 

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There is also a third problem in some areas where the limited availability of LNG bunkering facilities can be an additional barrier to adoption. Despite these challenges, LNG offers a great opportunity for vessels to reduce emissions and is widely seen as a good first step towards decarbonisation.


10. LNG is often described as a transition fuel. What does this mean?

LNG is often described as a transition fuel because it provides a good first step towards other alternative fuels. Sustainable fuels will be crucial to maritime decarbonisation, but the current cost, limited availability and insufficient infrastructure can make them a challenging choice for operators. 

Converting to LNG is a concrete step towards decarbonisation that vessel owners can take today, helping them to reduce emissions and comply with increasingly strict regulations. Conversion also opens up the possibility to use bioLNG and, eventually, synthetic methane.


11. What are the CO2 emissions from LNG?

LNG produces about 20–30% less CO2 when burned compared to traditional marine fuels like heavy fuel oil (HFO). The exact reduction in CO2 emissions depends on things like engine type, operating conditions and the specific composition of the LNG fuel.

Burning LNG releases about 2.75 kg of CO2 per kg of fuel, while HFO emits around 3.15 kg. While there have been some concerns about methane slip, the latest LNG engine technologies and best practices in LNG handling and storage can help minimise this. Additionally, using bioLNG, which is produced from organic waste, can further reduce the carbon footprint of ships that use LNG as fuel.

While LNG is not a zero-carbon fuel, it does offer a significant reduction in CO2 emissions compared to traditional marine fuels. This gives LNG an important role to play in the shipping industry's decarbonisation efforts until fully renewable alternative fuels are more widely available.


12. What are the lifecycle emissions from LNG?

The lifecycle emissions of LNG depend on factors like methane slip during production and transport, energy sources used for liquefaction and engine efficiency.

LNG produces 20–30% less CO2 when burned compared to heavy fuel oil, but methane slip can negatively offset this benefit. Engine manufacturers like Wärtsilä have been working hard to reduce methane slip. Since 1993, the methane slip from Wärtsilä dual-fuel engines has been reduced by around 90%, taking it from 16 grams per kilowatt hour (kWh) to less than two grams today. Wärtsilä is working on reducing methane slip even further, to less than 1 gram per kWh. When running an engine at optimal load, methane slip can now be minimal.

While Wärtsilä is focusing on reducing tank-to-wake emissions through engine development, producers are working to minimise well-to-tank emissions. They are doing this by investing in carbon capture, using renewable energy to decarbonise energy-intensive processes like liquefaction, and closely monitoring pipelines for emissions.

The shipping industry contributes just 2% of global CO2 emissions but 12% of SOx emissions and 13% of NOx emissions. Switching to LNG as an alternative fuel for shipping reduces emissions across the board, cutting NOx emissions by 85–90%, reducing particulate emissions and completely eliminating SOx emissions.

According to a study by the International Council on Clean Transportation (ICCT), the lifecycle greenhouse gas emissions of LNG can be up to 15% lower than those of heavy fuel oil when considering a 100-year timeframe. Using bioLNG, which is produced from organic waste, can significantly reduce lifecycle emissions, as the CO2 released during combustion is offset by the CO2 absorbed by the organic matter when it is growing.


13. What is the outlook for LNG availability?

The global LNG market is expected to grow significantly in the coming years, driven by increasing demand for cleaner energy sources. According to a report by Shell, the global LNG trade is projected to rise by 21% by 2025 compared to 2020 levels. The expansion of LNG bunkering infrastructure, with 235 ports offering LNG refuelling by 2025, is making LNG more accessible for the shipping industry. 


14. Do LNG tankers use LNG as fuel?

Many modern LNG tankers use LNG as fuel for ship propulsion and auxiliary power generation. These vessels are often referred to as LNG-fuelled LNG carriers. As newer LNG tankers enter the market and older vessels are phased out, the proportion of LNG tankers using LNG as fuel is expected to increase. This is for three main reasons:

  • Environmental benefits: By burning LNG instead of traditional marine fuels, LNG tankers can significantly reduce their SOx, NOx and PM emissions. This helps shipowners comply with increasingly stringent environmental regulations, such as the International Maritime Organization's (IMO) global sulphur cap.
  • Boil-off gas management: LNG tankers are designed to carry liquefied natural gas at cryogenic temperatures. Despite advanced insulation, some LNG will inevitably evaporate during transport, creating boil-off gas. By using this boil-off gas as fuel, LNG tankers prevent it from being released it into the atmosphere.
  • Fuel efficiency: The modern dual-fuel engines used on LNG tankers can operate efficiently on both LNG and traditional marine fuels like HFO, providing flexibility in fuel choice and optimising fuel consumption.


15. How many ships use LNG as fuel?

In 2024 there were more than 2,400 vessels equipped to operate on LNG globally, with another 1,000 LNG-fuelled vessels on order. These include over 20 cruise ships – many of which are using Wärtsilä LNG solutions – as well as tankers, containerships and RoRo ferries.

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16. Why is LNG an attractive prospect as an alternative marine fuel?

LNG is an attractive alternative marine fuel because it has a lower environmental impact than HFO. It produces significantly less SOx, NOx and particulate matter emissions, helping ships meet stricter regulations. Using LNG as fuel can also reduce CO2 emissions by 20–30% compared to heavy fuel oil.

Additionally, LNG is cost-competitive and increasingly available worldwide, with a growing number of bunkering ports. As the shipping industry seeks to decarbonise, LNG is seen as a viable transitional fuel until alternative fuels like green methanol and carbon-free green ammonia become widely available.


17. Is LNG the future of shipping?

LNG is already playing a significant role in the shipping industry’s transition to cleaner fuels. Its lower emissions and increasing availability make an LNG fuel system an attractive option for many shipowners.

As the industry works towards the IMO's goal of reducing greenhouse gas emissions by at least 50% by 2050, LNG is seen as a transition fuel, paving the way for the adoption of alternative fuels like green methanol and carbon-free green ammonia. This makes investing in flexible dual-fuel engine technology the safest path forward, using LNG as a first step towards a carbon-free future.

Hungry for more ways to reduce your greenhouse gas emissions? Discover 50 great ways the maritime industry could reduce greenhouse gas emissions, brought together in one handy eBook.

Written by
Amanda Thurman

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