You earn experience points from every fight you are matched up with, even those outside of missions.

If you are fighting another RP character the experience points given are: Winner recieves 20 experience points, loser recieves 10 experience points. However, the battle must be fought out to the full, and there must be a clear winner via the opponent losing their HP before the experience points can be gained.

If you are fighting a NPC character, its statistics, including the experience gained if beaten will be posted either, in the mission you are participating in, or in the NPC Archive section of the forum.

If you are participating in a mission which states you will gain experience points as a reward for mission completion, you gain only these experience points stated and not the experience points listed above if you fought a RPC or NPC during the course of the mission.

Contests, such as Battle Royales (all on all battles), count as only one battle and therefore when you get knocked out of the contest you recieve the 10 experience points unless the rules of the competition state otherwise. So if you win the battle royale you recieve 20 experience points.