Minecraft wiki entry for Drops, associated text: Experience orbs drop only if a mob dies less than three seconds after being attacked (melee, bow, snowballs, eggs, and potions causing instant damage) by a player or by a player's pet wolf, though not by a player-activated dispenser. Their total value is the specific amount of experience granted by killing that mob. They are also dropped from a thrown bottle o' enchanting. Collected experience accumulates into levels, which can be used for enchanting or repairing.