Minecraft wiki entry for Experience_farming, associated text: A mob farm can be built to let players finish off the mobs themselves, thus gaining the experience from the kills. Normally these will be oriented toward hostile mobs; Blazes have especially high experience value, and convenient spawners in the Nether that can be customized. Most hostile mobs will grant 5 XP apiece, with occasional bonuses for zombie variations and skeletons. Blazes give twice that, but without bonuses. Going from level 0 to 30 requires killing 279 "common" enemies, neglecting the bonuses.