A post from Star Wars: The Old Republic's Damion Schubert gave some insight on balancing XP gains for solo and group players:
We increase the XP pool for each group member in it, and then divide that pool. I don't have the number in front of me, but its something we'll be tweaking as we play anyway.
The general gist is that we want to reward grouping, but not so much that grouping is the only way to play the game (something that is very easy to do if you tilt the table too much, and then balance the levelling curve to that rate gain). That being said, as some have mentioned, grouping with another person increases your killing efficiency and reduces your risk of death substantially, to the degree that being in a group of two is vastly more efficient than 2X killing efficiency (this is like most MMOs). Still, you want to reward grouping enough to help ensure that you overcome the friction associated with grouping (finding groupmates, getting to them, tolerating idiots, etc).
Yes, we have anti-twink measures. Yes, high level players get shut out if they kill creatures too far below them. This is a fine line - you want to let high level players help their new friends, but you really don't want high level players hunting in low level areas, as that can be disruptive to the lowbies.
Yes, compared to other MMOs, we give you more XP for completing quests and less for killing creatures. These numbers will also likely be continually tweaked.
Yes, harder things give more experience.
Quote: Originally Posted by Xavior Group of 5 level 10's killing a level 10 mob: 100 xp each Group of 3 level 10's killing a level 10 mob: 100 xp each Solo person of level 10 killing a level 10 mob: 100 xp
no one gets screwed, no one is forced to group and everyone is happy.
Balancing it's not that easy. Instead, you need to look at XP gain per hour. A group of 3 can kill (let's say) 5X the creatures than a solo player can in an hour, which means that if you give everyone the full XP value, grouping is 5X() more efficient than soloing. If you balance the curve to that, the solo player gets screwed.
In our curve, we push that towards being closer to 2-3X. Still a significant advantage, but the grouper has to deal with all of the inertia of forming a group.