A drop tank is a external fuel tank carried by aircraft for long-range flights. It is designed to be discarded when empty or in the event of combat or emergency.

The drop tank was first used during World War II to allow fighter aircraft to carry additional fuel for long-range escort flights without requiring a dramatically larger, heavier, less maneuverable fuselage. Such tanks are now commonplace on military aircraft and occasionally for civilian use, although civilians are less likely to discard tanks except in the even of extreme emergency.

The problem with drop tanks is that they impose a drag penalty on the aircraft carrying them. A rule of thumb is that only about half the capacity of a streamlined drop tank actually goes towards increasing the aircraft's overall range, the rest going to overcome the added drag of the tank itself. The use of drop tanks also reduces the number of external hardpoints available for weapons, and increase the aircraft's radar signature, both problematic for modern tactical aircraft.