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LNG-fuelled sea-going vessels at anchor near terminal during dusk

LNG in Maritime Shipping: Emission Performance and Limitations in 2025

Author: Jeroen Berger • Publication date: June 22, 2025

Since the revision of MARPOL Annex VI (2021) and the phased implementation of the FuelEU Maritime Regulation (Regulation (EU) 2023/1805), liquefied natural gas (LNG) has regained attention as an alternative fuel for maritime shipping. LNG is internationally recognized as a transitional fuel: depending on engine type and combustion method, it can significantly reduce emissions of sulfur oxides (SOx), nitrogen oxides (NOx), and particulate matter (PM). Moreover, it can be deployed without fundamental modifications to existing engines, storage tanks, or bunkering infrastructure. At the same time, LNG faces structural limitations, including methane slip and limited CO2 reduction under suboptimal engine configurations.

This article outlines the factual status of LNG in 2025 in terms of emission performance, market volume, technical applicability, and legal compliance.

Emission Performance and Market Development

Since 2014, LNG has been considered one of the most technically mature alternative marine fuels, particularly in deep-sea shipping, ferry operations, and cruise services. In 2024, Shell delivered approximately 1.1 million tons of LNG for maritime applications globally, distributed across nearly 1,000 bunkering operations in 26 ports across 12 countries—doubling the volume delivered in 2023.

When combusted, LNG emits virtually no sulfur oxides (SOx), while soot formation and particulate matter emissions are also minimized. Depending on engine type, nitrogen oxide (NOx) emissions can be up to 80% lower than those of traditional HFO-fueled engines. Under ideal operating conditions, CO2 reduction reaches approximately 15–23% per ton-kilometer, influenced by engine configuration, loading factor, and operational sailing profile.

Market Share and Operational Application

Despite its emission advantages, LNG remains a niche fuel within the global bunkering industry in 2025. In Rotterdam—the Netherlands’ principal port and Europe’s largest bunkering hub—LNG accounted for approximately 3% of total bunkered volume in 2024. A total of 0.94 million m3 of LNG was delivered, representing a 52% increase compared to the previous year. In comparison, conventional fuels such as VLSFO and MGO collectively represented over 65% of market share.

Globally, the LNG-powered fleet is estimated to comprise 400 to 500 seagoing vessels, primarily operating in deep-sea container shipping, roll-on/roll-off services, and the cruise sector. Shipowners such as CMA CGM and Carnival Cruise Line utilize LNG to comply with the emission limits under MARPOL Annex VI, including the sulfur cap (Reg. 14) and the Tier III nitrogen oxide standard (Reg. 13). According to Shell’s market analysis, the number of LNG-fueled vessels could exceed 2,000 in the coming years, based on current newbuilding orders.

Limitations: Methane Slip and Well-to-Wake Emissions

A persistent concern with LNG is methane slip—the release of unburned methane (CH4) during the combustion cycle, especially in low-pressure dual-fuel engines operating on the Otto cycle. Since methane is more than 80 times more potent than CO2 as a greenhouse gas over the short term, this emission can significantly undermine LNG’s potential climate benefits.

As a result, total well-to-wake emissions of LNG are highly dependent on engine type, combustion method, and operational conditions, and do not in all cases present an improvement over conventional fuels such as HFO or MGO.

Technical Compatibility with Bio-LNG and Synthetic Methane

Despite these limitations, LNG remains a strategically deployable transitional fuel in 2025. Existing cryogenic infrastructure and engine technologies are fully compatible with bio-LNG and synthetic methane—fuels that are molecularly identical to fossil LNG and potentially climate-neutral, provided they are produced using renewable energy and certified feedstocks.

As fully drop-in alternatives, bio-LNG and synthetic methane can be applied directly within existing LNG value chains, without the need for retrofitting, engine recalibration, or modifications to onboard bunkering systems. This technical compatibility positions LNG as a scalable bridge technology toward low-emission and, ultimately, climate-neutral shipping.

Conclusie: LNG als brugtechnologie binnen de energietransitie

Between 2014 and 2025, LNG has evolved from a technological promise to a modestly adopted alternative. Despite its limited global market share, the growth in volume—including a record 1.1 million tons bunkered globally and a 52% increase in Rotterdam—demonstrates that LNG is gaining traction within specific vessel segments.

In 2025, LNG represents a practically viable pathway to emission reduction, without requiring modifications to ships or port infrastructure. Provided it is carefully applied and combined with the use of bio-LNG or synthetic methane, LNG offers a realistic stepping stone toward low-emission and eventually climate-neutral maritime shipping.

Frequently Asked Questions about LNG in Maritime Shipping in 2025

LNG fully eliminates sulfur oxides (SOx), reduces particulate matter (PM) by over 95%, and cuts nitrogen oxides (NOx) emissions by up to 80%, provided the engine is a high-pressure dual-fuel system with direct injection operating on the Diesel principle. At engine loads of at least 75% MCR, with accurate tuning and a stable operational profile, CO2 emissions can be reduced by 15 to 23% per ton-kilometer. These values must be verified per engine type, based on ISO 15016 and validated operational measurement data.

Yes. LNG inherently complies with Regulation 14 of MARPOL Annex VI (2021), as the fuel contains no sulfur. When combined with a Tier III-certified dual-fuel engine and, where required, additional exhaust gas aftertreatment—such as a Selective Catalytic Reduction (SCR) system or an Exhaust Gas Recirculation (EGR) system—it also meets the NOx emission limits under Regulation 13.

An SCR system reduces NOₓ by injecting urea into the exhaust stream, while an EGR system recirculates part of the exhaust gases into the combustion chamber to lower peak temperatures. Certification must be carried out in accordance with the NOx Technical Code (2008), evaluating the entire propulsion system based on type approval, measurement protocol, and in-operation emission performance.

Methane slip represents a structural emission source in low-pressure dual-fuel engines operating on the Otto cycle. During pre-ignition or at low loads, unburned methane (CH4) may be released via the exhaust system or crankcase. Given that CH4 has a Global Warming Potential of approximately 82 (20-year horizon, IPCC AR6), methane slip can significantly undermine LNG’s climate benefits. Measurements on LPDF four-stroke engines indicate an average methane slip of roughly 6.4% of fuel input, substantially reducing theoretical climate advantages.

Yes. Bio-LNG is produced from organic waste via anaerobic digestion and cryogenic purification. Synthetic methane is generated from green hydrogen and CO2, for example through the Sabatier reaction. Both are chemically identical to fossil LNG, allowing direct use in existing cryogenic tanks, bunkering systems, and dual-fuel engines without modifications or retrofits. This full drop-in compatibility is recognized under FuelEU Maritime (Regulation (EU) 2023/1805), provided the fuels are demonstrably certified as sustainable.

The total climate impact of liquefied natural gas (LNG)—from extraction and distribution to onboard combustion—varies considerably. When fossil LNG is used in combination with methane slip, total greenhouse gas emissions expressed in carbon dioxide equivalents (CO2-eq) may equal or even exceed those of Very Low Sulphur Fuel Oil (VLSFO) or Marine Gas Oil (MGO).

Conversely, the use of bio-LNG or synthetic methane can enable near-zero emission performance, provided these fuels are produced with renewable energy and certified non-fossil carbon sources. An objective assessment of climate performance requires a full Life Cycle Assessment (LCA) in accordance with ISO 14040 and ISO 14044.

LNG is cost-effective for shipowners operating on emission-critical routes—such as Emission Control Areas (ECAs)—with access to a robust bunkering infrastructure and a strategic focus on compatibility with bio-LNG and synthetic methane.

Despite relatively high upfront investments, LNG offers immediate compliance with MARPOL Annex VI, eligibility under the European Emissions Trading System (EU ETS 2024), and technical compatibility with bio-LNG and synthetic methane. Economic viability depends on factors such as methane slip, fuel pricing, fleet scale, and the modular or future-ready design of existing systems.