Fuel is a type of ammunition found only in Chapter 6 of Metro 2033 Redux, the Metro: Last Light DLC, Developer Pack, in the Spider Lair mission and the Developer Pack level. It is used only in the Flamethrower. Before the Redux version comes out, the fuel is not consider as ammunition and player has infinite when available.
Though the type of fuel is not specified, it appears to be a gaseous fuel, most likely propane - flamethrowers normally use a liquid fuel and do not actually throw flames, but coat the target in burning liquid; the Metro flamethrower is an exception in that it actually does throw fire, hence its very short range. The gas is stored in a tank on the users back and connected to the flamethrower with a hose, where it is ignited with a spark device.
Aside from finding uses in weaponry, the people of the metro value fuel extremely high considering it can be used to power generators which in turn provide the metro with electricity. Fuel also is used to power motor Vehicles which gives it high barter rates among travelers who can afford such luxury.
- The fuel is used by enemy in another way, the gasoline cans are used by the enemy as wired trap.