|Experience gained from defeating an NPC is determined by a dynamic experience economy, which allocates experience according to how frequently that NPC is defeated. Each time you defeat an NPC their value goes down, and their experience is redistributed to other NPCs in the game.|
The result of this system is that frequently defeated NPCs will be worth relatively little compared to those less frequently challenged. If you find that your victories are no longer worth as much experience as you would like, perhaps it is time to explore, and step off the beaten path to hunt fresh targets.
The total amount of experience in the game always stays the same, so you do not need to worry about depletion or inflation over time due to changing frequencies of player-vs-NPC defeats worldwide.