The release of greenhouse gases from underground coal-mine fires is a function of temperature and the concentration of O₂. In a laboratory study on spontaneous combustion, samples of coal, coal refuse, and carbonaceous shale were heated at a controlled rate between ambient temperature and 250 °C. In these experiments, the concentration of O₂ was not limited and the concentration of CO₂ increased with increasing temperature to a maximum of 10%. Carbon monoxide was not detected at temperatures below 100 °C, and the maximum concentration of CO was less than 4%. In field studies, samples of combustion gases were obtained from fires in three abandoned coal mines. These indicated a linear increase in the concentration of CO₂ relative to the decreased concentration of O₂. At an O₂ concentration of 2%, the CO₂ concentration approached 15%, and CO was detected only when the O₂ concentration was less than 8%. At temperatures over 50 °C, the rate of desorption of CH₄ also increased, but the average concentration in the mine atmosphere was 0.20%.

These laboratory experiments and field studies indicate that the rate of gas production is controlled by O₂ concentration and temperature, but physical factors, such as overburden fracturing and differences between surface and subsurface temperature and pressure, control the rate of emission to the atmosphere. In coal-mine fires, both chemical and physical factors control the rate and magnitude of contributions to the atmospheric concentration of greenhouse gases.