The American Association of Petroleum Geologists (AAPG) is one of the world's largest professional geological societies with more than 40,000 members across 129 countries as of 2021. The AAPG works to "advance the science of geology, especially as it relates to petroleum, natural gas, other subsurface fluids, and mineral resources; to promote the technology of exploring for, finding, and producing these materials in an economically and environmentally sound manner; and to advance the professional well-being of its members." The AAPG was founded in 1917 and is headquartered in Tulsa, Oklahoma; currently almost one-third of its members live outside the United States.