Spare Planes: How Many Do Airlines Have On Tap?

How many reserve planes are typically lying around in airlines? Not many. Airlines can’t function like the Air Force and have numerous expensive jets lying around “just in case.” Still, aircraft breakdown and mishaps happen while political/weather/other factors may ground their aircraft. Airlines are also called on to perform rescue flights when a crisis breaks out (these aircraft need to be pulled form somewhere). In these situations, airlines may need to call on another aircraft—but do they have reserve planes lying around?