Air Evac EMS, Inc., operating as Air Evac Lifeteam and sometimes called simply Air Evac, is an American helicopter emergency medical service (HEMS) or air ambulance provider headquartered in O'Fallon, Missouri. It is the largest subsidiary of Global Medical Response, though still considered an independent provider. It is also the largest membership-supported air ambulance service in the US operating helicopters from 140 bases in 15 states, mostly in the central and southern regions of the country. While primarily a HEMS provider, it also operates 2 fixed-wing aircraft in Missouri and Kentucky.