Quest XP is fixed, with a couple of caveats. The XP you get is dependent on the level the quest shows at in the Journal, so most quests will always give the same XP reward regardless of your level because the quest level is fixed. The only time this doesn't apply is if you complete a quest that is 5+ levels above your level, in which the XP reward will be capped at that of 5 levels up. So if you are Level 30, and you do a Level 37 quest, you will only get an XP reward appropriate to a Level 35 quest. There are also some quests which scale with you, and the XP reward for those quests will scale with you as well.
Each quest has an internal "difficulty" which defines a multiplier applied to the XP reward; so a standard Level 30 quest will give 2447 XP, while an easier Level 30 quest will give 1835 XP, and a very hard Level 30 quest will give 5505 XP. Note also that the maximum amount of XP you can receive in one hit is 10% of XP-to-level, so if you are Level 30, the amount of XP required to reach Level 31 is 48,080. This means that completing that Very Hard Level 30 quest at Level 30 will only give you 4808 XP, not the 5505 XP it would otherwise give.
Came in to post. Saw @enodoc already nailed it. Left thread.
-First-Wave Closed Beta Tester of the Psijic Order, aka the 0.016 percent. Exploits suck. Don't blame just the game, blame the players abusing them! -Playing since July 2013, back when we had a killspam channel in Cyrodiil and the lands of Tamriel were roamed by dinosaurs.
________________ -In-game mains abound with "Nerf" in their name. As I am asked occasionally, I do not play on anything but the PC NA Megaserver at this time.