Can someone explain this?

[Jessweeee♪]

I like my party to be totally and completely equal, so that all three girls level up after the same battle. Problem is, Paine seems to level faster than Rikku, and Rikku faster than Yuna (slowpoke).

Every once in awhile, I'll get out the Lady Luck dresspheres with the Double EXP to get them totally even, but then slowly they get unbalanced again >.<

Nobody's dying in battle, so they're all recieving EXP. Is this because Paine and Rikku need less EXP to level than Yuna, or is there some other factor that decides how much EXP a party member gets?

[Tavrobel]

Paine and Rikku get those few extra battles of EXP at the beginning of the game. Yuna (if you bothered) should catch up when you do Den of Woe as she fights against Rikku and Paine for EXP. However, there is also that Rikku's maximum EXP requirement for level 99 is lower than everyone elses, and Paine's is lower than Yuna's (or some other way around, who cares?).

I don't know the actual numbers, but they have a discrepancy of about 100k (from what I can tell).

[Little Blue]

The initial battles have nothing to do with it, its all probably down to the scaling of the levels due to that discrepancy you mention Tavrobel.

I wouldn't worry so much about them being equal to be honest Jessweeee♪. I can't remember if there are any multi-character level sensitive attacks in this game, but I'll just assume there is and if you have the girls at the same level you run the risk of them all being KO'ed. Course, that assumption could be complete crap and you've got nothing to worry about except a little extra effort where none is really needed to be honest...

[Tiamat3710]

the experience for yuna to level up is higher than rikkus and paines for some reason they will all end up 100 anyway