DannMann brings up a good point BUT I have to say that other game\'s ideas for dealing with this possible problem aren\'t the best IMHO.
Level systems based on XP often allow devs to make simple rules about who can group with who - for example, a player 10 levels under another player will recieve no XP - this is ok, but there are tons of reasons why this is bad. For one it\'s just plain fun to group with people way stronger than you, especially if your a newbie. Another reason is the realism of the whole idea - in rl lets say you are a beginner taking a walk with your teacher of (insert some martial art here) a gang a punks jumps you in an alley and demands your wallets, your teacher isn\'t going to do that for whatever reason and kicks the crap out of the guys, you don\'t do much, or maybe you do nothing, but just witnessing this feat gives you experience - you can\'t reproduce the feeling of being jumped in the dojo - well, maybe you can, but that\'s a different thread.... Also, even the act of observing what your teacher does can help you out.
I could continue with the little narrative but I\'m sure you get the point by now (or at least I hope you do) Now, you might be saying, \"Ok, ok Snow, that\'s all good but how else do you do it?\" Glad you asked. One way you might do it would be to create an algorithm that considers a number of different factors via a number of different equations. Some factors might be...
-The difficulty level of a NPC/MOB
- How long was the encounter?
- What, if any, where the complications?
- Has the PC seen the NPC/MOB type before?
- Anything else you guys can think up
Now to explain these guys
*Difficulty*
This is the big one, that requires the most thought, and maybe even an actuary, lol

[gotta love the humor]
WAIT! I know what you\'re thinking and no we are not back to square one with the level - yes or no thing. The outcome of a battle cannot be based on a single stat alone - esp experience. Thinking like that leads to problems like, \"If the PC is really strong but too slow to hit the target is he really all that strong?\" and the reverse \"If a PC is fast enough to land 6 hits in the blink of an eye, but each only takes 1/10 of a hit point, are they going to stand up to someone with tons of stamina? Like lets say Rocky for example...\"
The way around this is an equation that determines the likelyhood of a PC beating a MOB. How you do this is with a large string of comparisons of stats. Who\'s faster? Ok, by how much? [what is the probablity of PC hitting MOB based on agility and vice versa] If those hits do connect how badass are they compared to the opponent\'s stamina and health points? [How many hits to a kill? If the slow guys only needs to connect ONCE the odds are better of him winning, then if it were 100 times - making the odds close to zero]
After those two big ones you might want to consider other party members and their strengths. This creates a tiny problem b/c you are calculating each PC indepently and since they are each considered in each others\' equations, you get a loop going back and fourth. This isn\'t really a problem because in the loop situation you are comparing each PC\'s powerlevel in COMPARISON to the MOB - I see you forgot (or maybe you didn\'t

) So, before hand to fix this you create a hierarchy of who is the strongest group member by having the algorithm pit the PCs in a fight against each other using the same equation as used in the PC versus MOB senario.
You can apply a similar methodology to multiple mobs by breaking up each fight into separate mini encounters....
At the end, you get a single value X where PC Alpha has an X% chance at dropping MOB Beta
*Encounter length*
This one is simple - Which leads to more XP in two battles between the same two forces - a shorter one or a longer one? This whole concept reflects the skill of the people fighting (Two people of equal strength fight, but one is MUCH more skilled at playing his/her character and annihilates the opponent in a couple of seconds VERSUS two equally matched fighters that duke it out for an hour)
This one leads to exploits b/c PCs could deliberately draw out battles for more XP - but seriously if someone really wants to do that, make it worth their time! Just make sure you make a note that even though the battle lasted an hour, the PC still had a 98.7% chance of winning...
*Complications*
-Did your Uber buddy leave the group stranded?
-Did your Healer die?
-Did a Caster draw hits?
etc - these are more flat out values that you would add XP for, or possibly scale the total value at the end....
*Have you seen this MOB?*
If you have faught a million tree lizards before, you are gonna know how they move, their weakspots, etc
So, if you haven\'t seen a MOB before you get bonus XP.
This idea presents problems with logistics because you\'d have to keep a list of what you\'d seen before.
OR you could rate the rarity of a mob and then reward XP that way.
*Put it together*
I\'m just going to use an example here.
TEST BATTLE: PC Alpha Versus Beta the Baddie
Alpha has a 72% chance of beating Beta
Fight lasts 15 seconds
Alpha is a Caster and takes a hit
Beta dispite his name, is a EXTREMELY RARE MOB
Details:
Alpha is slighty faster than Beta and has decent attack power when compared to Beta\'s Stamina and HPs
However, Beta is only slightly slower and can probably kill Alpha with two or three hits...
Alpha defeats beta but takes a longer than expected amount of time for the 72% chance of winning - however it does not appear the amount of time was TOO much suggesting a drawn out battle [this wouldn\'t be a cut off, but a curve of the 4th power most likely]
XP
since Alpha had a decent chance of winning ...... 50 XP
A little extra time on the field [add ten percent] *1.1
Caster takes hits [flat bonus] ............................ +3
Beta\'s Rarity [flat bonus] ................................... +20
--------------------------------------------------------------------
78XP
Well there it is, just an example of a more complicated XP system. Any other ideas out there? Changes? Requests that I keep the post size down, lol?