For this annual report, GHG are defined as:
carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF₆). The primary sources of these gases are:

CO₂ — Combustion of fossil fuels and industrial processes

CH₄ — Landfills, coal mines, oil and gas operations, and agricultural activities

N₂O — Agricultural activities, combustion of fossil fuels and industrial processes

HFCs, PFCs and SF₆ — Industrial processes and leakage

Source: Energy Information Administration, U.S. Department of Energy