The massive perturbation to global climate and the carbon cycle during the Paleocene/Eocene Thermal Maximum (PETM) (approx. 55.5 Ma) may have been forced by a catastrophic release of methane gas (CH₄) from hydrate deposits on the continental slope. We investigate whether reported PETM paleotemperature and paleo-CO₂ proxies are consistent with this hypothesis by considering the impact of large increases in CH₄ emissions to the atmosphere. Significant effects on atmospheric chemistry and CH₄ lifetime are seen for a range of plausible emission rates (1500 Gt carbon over 500–20,000 years). The resulting peak anomalous radiative forcing is 1.5–13.3 W/m² depending on the emission scenario. The scenarios most closely matched to the PETM carbon isotope excursion have peak forcing of around 3 W/m², which translates to peak temperature changes as a function of latitude that are a reasonable match to derived estimates. High CH₄ levels and enhanced stratospheric water vapor amounts persist for as long as do the emissions and are responsible for more of the peak radiative forcing than CO₂ levels, although results are sensitive to the background climate state and base CH₄ concentration.