Biomethane’s Dirty Secret: Loss Rates Beat Fossil Gas
Biogas and biomethane are often billed as cleaner stand-ins for fossil gas, but a sweeping analysis suggests their methane leaks are bigger than many think. By pooling on-site and whole-site measurements from dozens of studies and running Monte Carlo simulations, researchers find that real-world emissions could be more than double earlier estimates. The heaviest losses cluster at the digestate stage—the handling and storage of leftover material after digestion—while a small group of “super-emitters” (about 5% of sites) accounts for roughly 62% of total methane released. Although total methane from biogas/biomethane is lower than from oil and natural gas, the percentage of gas lost is higher, threatening climate gains unless targeted fixes are deployed.
Biogas and biomethane promise lower-carbon energy by turning organic wastes into useful fuel. But methane—the fuel itself and a powerful greenhouse gas—can escape at multiple points along the chain. A new synthesis led by researchers at Imperial College London stitched together field measurements from the literature and used Monte Carlo modeling to map where emissions really arise. Their verdict: leaks are larger and more unevenly distributed than inventories imply.
The biggest hotspot is digestate handling. Open or poorly covered tanks and lagoons allow methane to form and vent after the main digestion step, driving a wide “heavy-tailed” distribution of outcomes. In practical terms, a small fraction of facilities—about 5%—produce roughly 62% of all observed methane losses. Production equipment (digesters, hygiene/buffer tanks) and certain upgrading systems contribute meaningfully too, while transmission and storage tend to be smaller sources.
Across thousands of simulated supply-chain runs, the team found median methane loss rates around five to six percent of biomethane produced—higher than typical loss rates reported for oil and natural gas. Total methane mass from the biogas sector remains below that of fossil fuel systems, yet the higher percentage loss erodes climate benefits because methane warms far more than carbon dioxide over the next decades.
The study also compared component-level modeling with whole-site mobile measurements and flagged reasons they can diverge: intermittent vents, process upsets, meteorology, and “miscellaneous” sources like biofilters and solids handling that aren’t always counted. Including such sources increased modeled totals by roughly a fifth. The authors argue that continuous or routinely repeated monitoring is essential to catch sporadic super-emitter behavior.
Solutions exist. Closing and properly maintaining digestate storage, fitting vapor-recovery to route residual gas back into upgrading, and prioritizing lower-leak upgrading technologies can drive rapid reductions. Given biomethane’s role in many climate pathways, the message is clear: its advantages depend on aggressive methane mitigation across every stage.