The total experience earned for killing a monster is divided evenly among all party members. The total experience earned for killing a monster is increased by 35% when a party member of the killer is in the same named area, defined as the “level” on the Automap. During v1.09, it was not difficult at all to rise from 90 to 99, and the fastest players reached level 99 in less than two days following some ladder resets in 20.
Leveling up past level 90 has become far more time-consuming since the v1.10 patch.