Fossil fuels surrender most of their carbon when burned , but GHGs are also emitted when coal is dug out of mines and when oil is pumped up from wells.
Additional quantities escape into the atmosphere when fuel is transported, as in gas pipelines.
Natural gas and oil often occur together in deposits. Oil drillers sometimes simply flare, or burn off, the gas or release it directly into the atmosphere, particularly if the well is too far from gas pipelines or potential gas users. Global emissions of CO2 from gas flaring reached a peak during the mid-1970s and have declined since. Gas that previously was flared is now increasingly captured for use as fuel due to higher prices and demand for gas, as well as improvements in production equipment. Methane is released when natural gas escapes from oil and gas wells and pipe fittings.