--- source_url: "https://north-standard.com/insights-and-resources/resources/articles/methane-slip" title: "Methane Slip | NorthStandard | Marine Insurance" mirrored_at: 2026-08-24T13:03:05.712Z host: north-standard.com cited_in_42a: true mirror_canonical: "https://index.42a.ai/north-standard.com/insights-and-resources/resources/articles/methane-slip" --- > **Original source:** https://north-standard.com/insights-and-resources/resources/articles/methane-slip #### How the industry is reducing methane from ships, a gas 28 times more potent than CO2. What is methane slip? ##### What is methane slip? Methane slip refers to the portion of methane in Liquefied Natural Gas (LNG) that is not burned during engine operation or auxiliary system use. Instead of combusting fully, this methane passes through the engine and appears in the exhaust stream as unburned gas.  Methane slip can also come from operational leaks, such as small releases during refuelling, purging of fuel lines, or other handling processes. LNG carriers may also need to flare off excess gas in certain situations for safety, typically when managing pressure risks.  Why is methane risk a concern? ##### Why is methane risk a concern?  LNG is considered by many as a transitional fuel on the pathway to a carbon-neutral maritime sector.  LNG produces significantly lower greenhouse gasses (GHG) compared with conventional fuels, with CO2 being the most significant. However, methane itself is a highly potent greenhouse gas, reported as having a Global Warming Potential (GWP) of 28 over a 100-year period, meaning it traps 28 times more heat than the same mass of CO₂. Over a 20-year timeframe, its GWP rises to 84, highlighting methane’s far stronger short-term impact.  Because of this, even relatively small methane leaks can have a disproportionately large climate effect, and excessive methane slip can cancel out most of the climate benefits that LNG is intended to provide.  What do the regulations say? ##### What do the regulations say?  At the global level, the IMO’s Net-Zero Framework which, while still under development at the time of writing, includes methane slip on a well-to-wake basis. The IMO’s life-cycle assessment expresses emissions as CO₂-equivalent (CO₂e) using the 100-year GWP values. To calculate methane slip, the IMO relies on default slip factors specified in [MEPC.391(81)](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.391%2881%29.pdf), although ship operators may use more accurate, vessel-specific measurements if they follow the verification guidelines in [MEPC.402(83)](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.402\(83\).pdf).  For the IMO’s short-term measures, such as the Carbon Intensity Indicator (CII), methane is not currently included. However, the regulation is scheduled for review in 2026.  In Europe, FuelEU Maritime aims to cut the GHG intensity of marine fuels by promoting renewable and low-carbon alternatives. It applies to ships over 5,000 GT calling at EU ports and covers CO₂, methane, and nitrous oxide, again on a well-to-wake basis. The first reporting period began in 2025, and methane slip is included in the calculation of GHG intensity.  Methane slip is also reportable under the EU Monitoring, Reporting and Verification (MRV) regulation, and as of 2026, it has been incorporated into the EU Emissions Trading System (ETS). Shipping companies are now required to surrender allowances not only for CO₂ but for methane and nitrous oxide emissions too.  How do the regulations calculate methane slip? ##### How do the regulations calculate methane slip?  Regulatory calculations use standard methane slip factors, shown in the table below. These values are not engine specific. Instead, they are based solely on engine type and operating speed, because these two factors largely determine how methane behaves during combustion.  The key distinction is the engine speed and whether an engine runs on an Otto-cycle or a Diesel-cycle:  - Otto-cycle engines ignite fuel using a spark and generally have higher methane slip because part of the air–fuel mixture can remain unburned.  - Diesel-cycle engines ignite fuel through compression heat, which leads to more complete combustion, resulting in lower methane slip.  By using these engine-type categories, regulators apply a consistent method of estimating methane slip across the global fleet, even though the actual performance of individual engines may vary.  Engine configuration Default methane slip % of consumed fuel LNG Otto (dual fuel, medium speed) 3.5% LNG Otto (dual fuel, slow speed) 1.7% LNG Diesel (dual fuel, slow speed) 0.15% LBSI (lean-burn spark ignition) 2.6% How can the amount of methane slip be improved? ##### How can the amount of methane slip be improved?  Engine designers and manufacturers have introduced technical developments that improve engine efficiency and therefore lower methane slip. Manufacturers claim some of these upgrades can reduce slip by up to 60%.  In addition, exhaust treatment solutions, such as palladium-based catalysts, can chemically remove methane from the exhaust before it is released. Engine optimisation and robust maintenance practices helps keep methane slip to a minimum too.   A modern slow speed LNG Otto engine, incorporating advanced technical improvements such as precise turbocharger (lambda) control to ensure the correct air–fuel mixture for LNG combustion, along with exhaust after-treatment solutions, has the potential to achieve lower methane slip compared with the standard 1.7% factor (see table above).  Modern LNG and dual-fuel engines have achieved up to 90% lower methane slip compared with the first generation of engines produced in the early 1990s.   How to apply methane slip values which reflect the individual engine? ##### How to apply methane slip values which reflect the individual engine?  Over the next decade, as compliance thresholds tighten, using actual methane slip values instead of default factors could deliver annual cost savings. These savings could result in surrendering fewer allowances under EU ETS, and a reduced deficit/increased surplus under FuelEU Maritime. In addition, this approach provides more accurate emissions data under EU MRV.  To apply actual methane slip factors under FuelEU Maritime, EU MRV and EU ETS, the European Commission has issued [guidance](https://transport.ec.europa.eu/document/download/9573f03b-a821-46ee-8131-312832b4ca32_en?filename=guidelines_for_reporting_and_verification_actual_methane_cslip_ef.pdf) detailing reporting and verification procedures. This guidance builds on IMO’s MEPC.402(83), which establishes principles for exhaust gas analysis, including methane slip.   The EU approach requires continuous engine load monitoring, with load values averaged over 30-minute intervals. These averages are then compared with methane slip values from established emission curves. The cumulative data over the calendar year is used to calculate the actual methane slip factor. Many engine manufacturers now offer automated monitoring solutions, some incorporating AI, to measure methane slip continuously and in real time.  Given the potential cost savings, especially on engines that have undergone technical upgrades, it is suggested to consider:  - Using actual methane slip readings on LNG and dual-fuel engines where possible.  - Consider upgrades or exhaust treatment solutions to reduce methane slip.  - Install systems for continuous engine load monitoring.  - Have the system and measurements verified and accredited by the vessels classification, and approved verifier, to ensure reported emissions accurately reflect the LNG engines true performance.  Further Resources #### Further Resources Our article, authored by [Mark Smith](https://north-standard.com/our-people/mark-smith), Loss Prevention Director - NNE and Decarbonisation "**LNG – From Waste to Wake**" focuses on Biomethane and how it compares to LNG and other fossil fuels and why it will become more widely used between now, 2030 and beyond. [**Read it here**](https://north-standard.com/insights-and-resources/resources/articles/lng-from-waste-to-wake) - [What is methane slip?](#what-is-methane-slip) - [Why is methane risk a concern?](#why-is-methane-risk-a-concern) - [What do the regulations say?](#what-do-the-regulations-say) - [How do the regulations calculate methane slip?](#how-do-the-regulations-calculate-methane-slip) - [How can the amount of methane slip be improved?](#how-can-the-amount-of-methane-slip-be-improved) - [How to apply methane slip values which reflect the individual engine?](#how-to-apply-methane-slip-values-which-reflect-the-individual-engine) - [Further Resources](#further-resources)