How the industry is reducing methane from ships, a gas 28 times more potent than CO2.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? 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? 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), although ship operators may use more accurate, vessel-specific measurements if they follow the verification guidelines in MEPC.402(83). 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? 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. 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-