Yes, cars produce methane, but in very small amounts. Internal combustion engines running on gasoline or diesel emit methane as a byproduct of incomplete combustion. Globally, road transport accounts for roughly 2 to 5 teragrams of methane per year, a tiny fraction of the 575 teragrams released annually from all sources combined.
How Car Engines Create Methane
Gasoline is a complex mix of hydrocarbons, and when it burns inside an engine cylinder, most of those hydrocarbons break apart and recombine into carbon dioxide and water. But combustion is never perfectly complete. In cooler zones of the cylinder, near the walls, and during the exhaust phase, hydrocarbon fragments called methyl radicals can recombine with hydrogen atoms to form methane (CH₄). This reaction occurs at intermediate temperatures, roughly 900 to 1,200 °C, where the fuel is hot enough to break apart but not hot enough for every fragment to fully oxidize.
Think of it this way: the engine is supposed to break fuel all the way down to CO₂, but some partially broken fuel pieces snap back together into the simplest hydrocarbon, methane, before they get the chance. The catalytic converter in your exhaust system destroys much of this methane before it leaves the tailpipe, but some still escapes.
How Much Methane Cars Actually Emit
The Global Methane Budget 2000–2020, published in Earth System Science Data, estimates that road transport and non-road transport each contribute about 2 to 5 teragrams of methane per year. To put that in perspective, total global methane emissions run around 575 teragrams per year, with roughly 65% coming from human activities. The dominant sources are agriculture and waste (about 228 teragrams per year) and fossil fuel extraction and processing (about 115 teragrams per year). Cars and trucks, by comparison, are a rounding error in the global methane picture.
That doesn’t mean vehicle methane is irrelevant. Methane is roughly 80 times more potent than CO₂ as a greenhouse gas over a 20-year window, so even small quantities matter more than they would for CO₂. But if you’re worried about methane specifically, livestock, landfills, and oil and gas operations are far larger contributors than the car in your driveway.
Gasoline vs. Natural Gas Vehicles
Standard gasoline and diesel cars produce relatively little methane because the fuel itself contains very little of it. Natural gas vehicles are a different story. Compressed natural gas (CNG) is almost entirely methane, so any fuel that escapes unburned, sometimes called “methane slip,” goes straight into the atmosphere. This can happen during fueling, through small leaks in the fuel system, or when unburned gas passes through the engine during cold starts or low-load driving.
The concern with natural gas vehicles has always been whether the methane that leaks offsets the CO₂ advantage of burning a cleaner fuel. Modern CNG engines and their catalytic converters have improved significantly, but the issue hasn’t disappeared entirely. For fleet operators choosing between gasoline and natural gas, the net climate benefit of CNG depends heavily on how well the fuel system and engine control methane losses across the vehicle’s lifetime.
How Regulations Address Vehicle Methane
The EPA regulates vehicle exhaust through its tiered emission standards, but it doesn’t set a separate limit for methane from gasoline cars. Instead, the standards focus on categories like “non-methane organic gases,” which covers the more reactive hydrocarbons that contribute to smog. Methane is less chemically reactive in the atmosphere when it comes to forming ground-level ozone, so regulators historically prioritized the other hydrocarbons.
This regulatory approach means methane from conventional cars has never been directly targeted the way nitrogen oxides or particulate matter have been. The catalytic converter reduces it as a side effect of cleaning up other pollutants, but there’s no specific gram-per-mile methane limit your car has to meet. For natural gas vehicles, some regulatory frameworks do account for methane more explicitly, since it makes up the bulk of their unburned fuel emissions.
The Bigger Picture for Drivers
If you drive a gasoline or diesel car, the methane coming out of your tailpipe is a negligible part of your vehicle’s climate footprint. Your CO₂ emissions from burning fuel are orders of magnitude more significant. The average gasoline car produces about 4.6 metric tons of CO₂ per year, while its methane output is measured in grams.
Where cars do contribute meaningfully to methane is upstream, not at the tailpipe. Extracting, refining, and transporting the petroleum that becomes your gasoline involves methane leaks at wells, pipelines, and refineries. Those upstream emissions are counted under the fossil fuel sector’s 115 teragrams per year, not under transport. So while your engine produces a tiny amount of methane directly, the fuel supply chain behind it is a much larger part of the methane problem.