LPG as an Alternative Marine Fuel
Which ships burn LPG, what the emission gains really amount to, the ME-LGIP engine, tank arithmetic, IMO interim guidelines, bunker supply and the long-term carbon targets.
LPG burns in dual-fuel marine engines, and at present nearly all the ships doing so are LPG carriers themselves, since the fuel is already aboard as cargo. The 2026 report from Lloyd's Register and the World Liquid Gas Association (WLGA) credits fossil LPG with about 97% less sulphur oxide, 90% less particulate matter and about 20% less CO₂ than heavy fuel oil (HFO).[1] Its role in decarbonisation is limited without bio-LPG or carbon capture, as it remains a fossil fuel.
DNV's Alternative Fuels Insight showed 172 LPG-capable ships in service and 147 on order in mid-2026, against 914 and 654 for LNG.[2] LPG and ethane orders reached 55 in the first half of 2026, up from 15 a year earlier.[3] Consumption remains small. IMO data put LPG at 242,292 tonnes in 2023 for ships of 5,000 GT and above, out of 211 million tonnes of fuel in total.[4]
Fuel Properties and Default Values
FuelEU Maritime assigns LPG a lower calorific value of 46.0 MJ/kg and combustion factors of 3.000 tonnes of CO₂ per tonne for propane and 3.030 for butane. The same dataset supplies the comparison below.[5]
| Fuel | LCV (MJ/kg) | Combustion CO₂ (g/MJ) | Well-to-tank (g CO₂e/MJ) | Well-to-wake (g CO₂e/MJ) |
|---|---|---|---|---|
| HFO | 40.5 | 76.9 | 13.5 | 91.7 |
| MGO | 42.7 | 75.1 | 14.4 | 90.8 |
| LPG, propane | 46.0 | 65.2 | 7.8 | 74.2 |
| LPG, butane | 46.0 | 65.9 | 7.8 | 74.9 |
| LNG, Diesel cycle, slow speed | 49.1 | 56.0 | 18.5 | 76.1 |
| LNG, Otto, medium speed | 49.1 | 56.0 | 18.5 | 89.2 |
Source: calculated from FuelEU Annex I and II values, with zero slip assumed for LPG.[5]
Reading the Published Percentages
These numbers explain why published reductions seem to disagree. On funnel CO₂ alone, propane beats HFO by about 15%. Well to wake, the margin widens to about 19% because the default upstream value for LPG is lower. Lloyd's Register's figure of about 20% and the up to 18% CO₂ reduction that Everllence, formerly MAN Energy Solutions, quotes for its ME-LGIP engine fall within that range.[1][6] The report also cites lifecycle savings of up to 17% against MGO.[1]
Comparison with LNG depends on the engine. LPG emits more CO₂ per unit of energy because propane has a higher carbon share than methane. Total emissions, however, also reflect upstream values and methane slip. On default figures LPG comes in well below a medium-speed Otto engine on LNG and slightly below a slow-speed Diesel-cycle engine. The regulation, however, lists LPG slip as not available and calls for a certified value,[5] so the LPG rows above rest on an assumption of zero.
The ME-LGIP Engine and Fuel System
MAN's two-stroke ME-LGIP was the first commercial marine engine designed to burn LPG. It injects the fuel as a liquid at high pressure and ignites it with a small pilot injection. A 2018 technical account gives an injection pressure of 500 to 600 bar and pilot fuel of about 3% in gas mode.[7] The maker reports more than 270 orders since 2018. The engine can change between VLSFO, MGO and LPG with no loss of performance, and ME-C engines with bores of 35, 50, 60 and 70 cm can be converted.[6]
Retrofits of existing ships did much to establish the technology. BW LPG began in 2018 with four engines and extended the programme in two steps during 2020 to cover 12 VLGCs.[8] The first ship, BW Gemini, was built in 2015 and has a capacity of 84,134 m³. At a Shenzhen yard her main engine was changed to a 6G60ME-LGIP, and Wärtsilä supplied the fuel system with two 930 m³ LPG fuel tanks. Trials began in October 2020, with expected savings of about 10% in fuel and 20% in greenhouse gases on the voyage to Houston.[9]
The case also shows why gas carriers went first. A VLGC already carries the fuel in its cargo tanks and already calls at LPG terminals. For other ship types the options are narrower. The Lloyd's Register report says engine choices beyond two-stroke are not yet fully mature,[1] which is a real restriction for auxiliary engines and smaller vessels.
Volume and Tank Arithmetic
At about 0.54 kg/L the liquid holds about 25 MJ/L, compared with about 40 MJ/L for HFO, so equal energy needs about 1.6 times the volume.[5] A ship burning 40 tonnes of HFO a day uses 40 × 40.5 = 1,620 GJ. Supplying that from LPG takes 1,620 / 46.0, or about 35 tonnes, which is about 65 m³ of liquid, against about 40 m³ of HFO. At that consumption the two 930 m³ tanks fitted to BW Gemini would last about 28 days, before any allowance for filling limits.
Propane's boiling point of −42 °C means LPG needs no cryogenic system of the LNG kind. It still requires pressurised or refrigerated tanks and dedicated space, and on a ship that is not a gas carrier that space comes out of cargo capacity.
Regulatory Framework
The IGF Code does not set out detailed provisions for LPG, so IMO has issued interim guidelines in two complementary documents.
| Document | Approved | Scope |
|---|---|---|
| MSC.1/Circ.1666 | MSC 107, June 2023 | Ships using LPG as fuel, following the structure of the IGF Code |
| MSC.1/Circ.1679 | MSC 108, May 2024 | Gas carriers using LPG cargo as fuel, relating to the IGC Code |
Source: IBIA; Hong Kong Marine Department.[10][11]
Both are interim, and the second is meant to apply until provisions enter the IGC Code. Approval runs through the flag state and class society. Bunkering remains a gap: IBIA notes that MSC.1/Circ.1666 does not cover LPG bunkering,[10] and the Lloyd's Register report describes the framework there as still developing.[1] The organisation behind these documents is described in the article on the International Maritime Organization.
Safety
The sharpest contrast with LNG lies in vapour behaviour. NIOSH figures put propane vapour at 1.55 and butane vapour at 2.11 times the density of air, with lower explosive limits of 2.1% and 1.6% by volume.[12] A leak tends to settle in bilges, engine room floors and pipe tunnels, and gas detection and ventilation have to be laid out with that in mind.
Spilled LPG largely evaporates and leaves none of the persistent film oil does, although the vapour cloud remains an ignition risk. More on the product itself appears under liquefied petroleum gas.
Supply and Bunker Infrastructure
The established trade network is one of LPG's main assets. Lloyd's Register cites more than 1,000 storage facilities and terminals, a record 145 million tonnes of seaborne trade in 2025 and over 1,600 LPG carriers in service. It suggests that around 500 terminals could supply other ship types with little new investment.[1]
That projection does not describe a working service network. Storing the product is one thing, and having a suitable barge, procedures and authorisation for ship supply is another. In practice most ships burning LPG draw on their own cargo.
Availability also responds to world events. Qatari LPG output suffered in the 2026 Gulf conflict,[13] and the Middle East produced 52.5 million tonnes in 2024.[14]
Carbon Targets and the Long Term
IMO's 2023 strategy seeks at least a 40% cut in CO₂ per transport work by 2030 against 2008 and net zero around 2050. Its checkpoints for total annual greenhouse gases are at least 20% by 2030 (striving for 30%) and at least 70% by 2040 (striving for 80%).[15] A gain of about 20% from fossil LPG helps with 2030 and falls far short of 2040.
FuelEU Maritime leads to the same conclusion. Propane's calculated 74.2 g CO₂e/MJ sits under the 2035 limit of 77.94 and above the 2040 limit of 62.90, and that assumes zero slip.[5] Hence the interest in bio-LPG and renewable LPG, which are chemically identical and can offer reductions of up to 80% according to feedstock.[1] Renewable LPG and DME capacity amounted to only 480,000 tonnes a year at the end of 2024.[14] The Lloyd's Register report also raises onboard carbon capture as a further route.[1]
Global enforcement remains undecided. Adoption of the IMO Net-Zero Framework was postponed for a year in October 2025. MEPC 85 is scheduled for 30 November to 3 December 2026, with the adjourned session resuming on 4 December, as of 3 November 2026.[16] For a gas carrier, burning LPG is a comparatively simple decision. For other ship types, fuel supply, tank space and engine choice change the calculation. Alternatives are compared under types of marine fuel and LNG-fuelled ships.
Frequently asked questions
How is LPG used as ship fuel?
LPG burns in dual-fuel marine engines, and at present nearly all the ships doing so are LPG carriers themselves, since the fuel is already aboard as cargo.
Does an LPG-fuelled ship meet the sulphur limits?
Yes. Everllence describes LPG as compliant with SECA rules, and SOx from fossil LPG is about 97% below HFO.
Are there IMO rules for LPG as fuel?
Yes, the interim guidelines MSC.1/Circ.1666 and MSC.1/Circ.1679. Application runs through the flag state and class.
Does LPG have methane slip?
Its main components are not methane, but unburned fuel cannot simply be assumed to be zero. FuelEU gives no default and asks for a certified value.
Can an existing ship be converted to LPG?
Suitable ME-C engines can be converted, as on BW Gemini. Tank location and fuel systems need assessing for each ship.
Sources
- Lloyd's Register. LPG Highlighted as a Practical Pathway to Accelerate Decarbonisation, press release, May 2026 (Fuel for Thought: LPG, with WLGA).
- ENGINE. LNG Leads Shrinking Alternative Fuel Vessel Orderbook in June: DNV, 3 July 2026.
- gCaptain. Alternative Fuel Ship Orders Surge in August as LNG Drives Strongest Month since 2024, 2026.
- International Maritime Organization (IMO). Report of Fuel Oil Consumption Data, Reporting Year 2023. MEPC 82/6/38, 26 July 2024.
- European Commission. Guidance on the FuelEU Maritime Regulation for Shipping Companies, 8 October 2025; Regulation (EU) 2023/1805, Article 4, Annexes I and II.
- Everllence (MAN Energy Solutions). ME-LGIP Product Page, 2026.
- Pospiech, P. Making the Case for LPG as a Marine Fuel. MarineLink, 16 October 2018.
- MarineLink. BW LPG Retrofits VLGCs, 2020.
- MarineLink. World's First LPG-Fueled Gas Carrier, 4 November 2020.
- IBIA. MSC 107 Approves Interim Guidelines for the Safety of Ships Using LPG as Fuel, 2023.
- Hong Kong Marine Department. Merchant Shipping Information Note 49/2024, 2 December 2024 (MSC.1/Circ.1679).
- US National Institute for Occupational Safety and Health (NIOSH). Pocket Guide to Chemical Hazards: Propane; n-Butane.
- Al Majalla. Can China's $3bn Loan to QatarEnergy Revive LNG Exports?, 2 November 2026.
- Argus Media. Q&A: Global LPG Growth Defies 2024 Headwinds, 16 September 2025.
- International Maritime Organization (IMO). 2023 IMO Strategy on Reduction of GHG Emissions from Ships.
- Ammonia Energy Association. MEPC84: Support for Net Zero Framework Stabilizes ahead of Key Decision Point in Late 2026, 2026.
