How Do Gas Carriers Work? The Complete Lowdown

Gas carriers are ships that have been specifically designed to transport liquefied gases safely across the globe. Unlike standard tankers, these vessels deal with cargo that must be kept at extremely low temperatures or under high pressure to remain in liquid form. 

From liquefied natural gas (LNG) that powers cities to the liquefied petroleum gas (LPG) used in everyday heating and cooking, gas carriers play a vital role in the global energy supply chain. Martide’s blog post looks at how gas carriers are built, how they operate, and what makes them unique. 

How Are Gas Carriers Constructed? 

Gas carriers are among the most technically advanced ships in the maritime industry. Their design focuses on maintaining their cargo in a liquid state under controlled conditions. 

Specialized Cargo Tanks 

The most distinctive feature of a gas carrier is its cargo containment system. 

There are three main types: 

• Membrane tanks: Thin, flexible tanks supported by the ship’s hull, commonly used in LNG carriers 

• Spherical tanks (Moss type): Large, round tanks visible above the deck, designed to handle pressure and low temperatures 

• Independent tanks: Self-supporting tanks used in smaller gas carriers 

These tanks are heavily insulated to keep their cargo at the required temperature. 

Insulation Systems 

Liquefied gases must be kept cold to remain in liquid form. 

• LNG is stored at around -162°C / -260°F 

• LPG is stored at around -50°C / -58°F or under pressure 

Insulation reduces heat transfer and limits evaporation of the cargo. 

Double Hull Structure 

Gas carriers are built with a double hull for added safety. This: 

• Protects cargo tanks from external damage 

• Reduces the risk of leaks in case of collision 

Cargo Handling Equipment 

Gas carriers are fitted with advanced systems, including: 

• Cargo pumps 

• Compressors 

• Vaporizers 

• Boil-off gas management systems 

These systems ensure safe handling of both liquid and gas phases. 

Read more: How Do Oil Tankers Work? A Complete Guide

How Do Gas Carriers Actually Work? 

Transporting liquefied gas requires careful control of temperature, pressure, and vapor. 

Liquefaction Before Loading 

Before being loaded onto the ship, gas is cooled or compressed into liquid form. 

• This reduces its volume significantly 

• Makes it practical to transport large quantities 

Loading Operations 

Cargo is loaded through insulated pipelines at specialized terminals. 

• Tanks are pre-cooled to prevent thermal shock 

• Loading is monitored to control pressure and temperature 

• Safety systems are always active due to flammability risks 

During the Voyage 

Even with insulation, some cargo naturally warms up and begins to evaporate. This is known as boil-off gas. 

Gas carriers manage this in several ways: 

• Using the gas as fuel for the ship’s engines 

• Re-liquefying the gas and returning it to the tanks 

• Safely venting small amounts if necessary 

Maintaining the right balance of temperature and pressure is critical throughout the journey. 

Unloading Cargo 

At the destination, cargo is transferred ashore. 

• Liquid gas is pumped out or vaporized depending on terminal requirements 

• Systems ensure safe transfer without leaks or pressure issues 

What Do Gas Carriers Transport? 

Gas carrier ships are designed to transport different types of liquefied gases, each with specific handling requirements. 

Liquefied Natural Gas (LNG) 

• Primarily methane 

• Used for power generation, heating, and industry 

• Requires extremely low temperatures 

Liquefied Petroleum Gas (LPG) 

• Includes propane and butane 

• Used in cooking, heating, and as fuel 

• Stored under moderate pressure or refrigeration 

Read more: How Do Chemical Tankers Work? A Practical Guide

Ethylene 

• A key chemical used in plastics production 

• Requires very low temperatures 

• Transported in specialized ethylene carriers 

Ammonia 

• Used in fertilizers and increasingly as a potential future fuel 

• Toxic and requires careful handling 

Other Gases 

• Propylene 

• Vinyl chloride monomer (VCM) 

• Butadiene 

Each cargo type determines the design and equipment of the vessel. 

Read more: Everything You Need to Know About LNG & LPG Tankers 

Where Do Gas Carriers Operate? 

Gas carriers operate on global routes, linking production areas with energy-hungry regions. 

Key Export Regions 

• Middle East (Qatar is a leading LNG exporter) 

• United States 

• Australia 

• Russia 

Key Import Regions 

• Europe 

• China 

• Japan 

• South Korea 

• India 

Major Trade Routes 

• Middle East to Asia (one of the busiest LNG routes) 

• United States to Europe and Asia 

• Australia to East Asia 

Gas carrier ships often operate on long-term contracts, ensuring steady supply chains. 

Types of Gas Carrier Ships 

Gas carriers vary in size and design depending on the cargo. 

• LNG Carriers – large vessels for the long-distance transport of LNG 

• LPG Carriers – these vessels carry propane, butane and similar gases 

• Ethylene Carriers – Highly specialized ships used for petrochemical gases   

• Small Gas Carriers – Used for regional or coastal transportation of gases 

Some Interesting Facts About Gas Carriers 

• LNG shrinks to about 1/600th of its original volume when liquefied 

• Some LNG carriers use boil-off gas as their main fuel source 

• Moss-type spherical tanks are designed to withstand extreme conditions and are visible above deck 

• Gas carriers are among the safest ships due to strict design and operational standards 

• The demand for LNG carriers has grown rapidly as countries shift toward cleaner energy 

Safety and Environmental Considerations 

Gas carriers operate under strict safety regulations due to the risks of flammable or toxic cargo. 

Key Safety Features 

• Gas detection systems 

• Emergency shutdown systems 

• Fire protection and containment systems 

Environmental Role 

While still fossil-based, LNG is considered a cleaner alternative to coal and oil, helping reduce emissions in the energy sector. 

At the same time, the industry is exploring future uses of gas carriers for transporting alternative fuels such as hydrogen and ammonia. 

The Future of Gas Carriers 

Gas carriers are expected to play an important role in the energy transition. 

• LNG is seen as a transitional fuel toward lower emissions 

• Ammonia and hydrogen may become key cargoes in the future 

• New ship designs are focusing on improved efficiency and lower environmental impact 

As global energy demand evolves, gas carriers will continue to adapt. 

Gas Carrier Ships FAQ 

Why do gas carriers need special tanks? 

Liquefied gases must be kept at low temperatures or high pressure, requiring specialized containment systems. 

What is boil-off gas? 

It is gas that naturally evaporates from the liquid cargo due to slight temperature increases during the voyage. 

Are gas carriers dangerous? 

They carry hazardous cargo, but strict safety systems and regulations make them very safe in practice. 

How long do gas carrier voyages last? 

Voyages can range from a few days to several weeks depending on the route. 

Can gas carriers transport different gases at once? 

Some smaller gas carriers can carry multiple cargoes, but large LNG carriers usually transport a single type of gas. 

 Gas carriers are a critical link in the global energy network. Their advanced design and precise operations allow them to transport essential fuels safely across vast distances, supporting industries and communities worldwide.