The Molotov Cocktail is a weapon featured in Resident Evil 0.
After getting an A rank in Leech Hunter (which unlocks infinite ammo for all weapons), a specific Molotov Cocktail can then be found in Room 201 of the Train in the main game that can be used indefinitely. Molotov Cocktails actually created even after getting the A rank will still have limited use.
Molotovs are fairly common. While effective against most enemies, they are singularly effective against a Mimicy Marcus, often destroying the mass of leeches after three attacks. However, they can be rather problematic to aim, and there is a short wind up animation before the cocktail is thrown. The splash will cause enemies within a short range to burst into flame, meaning there is a reasonable margin for error. Rebecca will use the Molotov Cocktails faster than Billy, so it's recommended to use them as Rebecca for more efficiency, although at the risk of taking more damage due to Rebecca's weaker health.