Here's the formula that is was copied from
Base experience per monster for players is the same as if they were playing solo, meaning a monster with 1000 base experience in solo play will have a base experience of 6000 in a party of 6, but the final amount received depends on player's level relative to party members and monsters
The usual experience penalty that can come from monster level applies, but experience is also redistributed to higher level characters. This is intended to balance the high experience requirements at higher levels. Monsters experience is awarded only to nearby (roughly two screens) party members
Each player's "share" of the experience gained is (CharacterLevel+10)^2.71. divided by the total of all players' shares.
For example, if a level 10 player was partied with a level 30 player:
- Level 10 player's share: (10+10)^2.71 = 3355
- Level 30 player's share: (30+10)^2.71 = 21957
- Total "Shares": 3356 + 21957 = 25313
Percentual Share of experience:
- Level 10 player would receive: 3355/25313 = 0.132 = 13.2% of the XP
- Level 30 player would receive: 21957/25313 = 0.867 = 86.7% of the XP