The D&D 3.5e DMG has the following for giving out exp:
To determine the XP award for an encounter, follow these steps.
Determine each character’s level. Don’t forget to account for ECL (see Monsters as Races, page 172) if any of the characters are of a powerful race.
For each monster defeated, determine that single monster’s Challenge Rating.
Use Table 2–6: Experience Point Awards (Single Monster) to crossreference one character’s level with the Challenge Rating for each defeated monster to find the base XP award.
Divide the base XP award by the number of characters in the party. This is the amount of XP that one character receives for helping defeat that monster.
Add up all the XP awards for all the monsters the character helped defeat.
Repeat the process for each character
Given rule 6, you do this for each character. This means it uses each characters ECL. If your group has level difference among party members, would the lower levels gain more exp than the higher levels? Or am I looking at this wrong?