Although the existence of XP, or Experience Points, is taken as fact by the characters (indeed, understood to be a natural law) in the Goblins universe, the amount of XP a character has (or how many more are needed for the next character level) is presumably theoretical. Characters tend to either be surprised by a level gain or to have only a general idea of how many more XP they need for the next level.
Characters will occasionally make comments regarding assumed XP gains from specific enemies. For example, Seth Bainwraith said, "And with the extra XP I'm gonna get for killing that metal thing, I'll be second level in no time!) Also, Fumbles said, "I bet a battle like that could knock me up to 3rd level and the rest of you to 2nd!"