A few assumptions:
- Somehow, no one dies (or the DM uses a house rule like one I've instituted lately, that the PLAYER earns the XP, and if a character dies, the replacement gets exactly the amount of XP the previous character had).
- We'll use the baseline XP per level of the Fighter, as it's close to the average of a party composed of 2 Fighters, 1 Cleric, 1 Thief, and 1 Magic-User.
- Any NPCs along for the ride are 0-level men-at-arms who don't get a share of XP, rather than henchmen who do.
- We'll assume, as Frank Mentzer wrote in the Masters Set, that approximately 80% of XP comes from treasure.
- The dungeon is filled using the B/X and BECMI d6 system for random dungeon stocking.
- Since my 5th level sparked the comments by Jarrah that got me thinking about this, it has 57 encounter areas, and the dungeon stocking method uses a d6, we'll assume a baseline of 60 encounter areas on each level.
OK, taking all these assumptions, what does that mean? Well, first of all, each level of the dungeon will contain:
20 Empty Rooms, 3 of which have unguarded treasure.
20 Monster Rooms, 10 of which have substantial treasure
10 Trap Rooms, 3 of which have unguarded treasure
10 Special Rooms, which typically have no treasures.
So that's 16 locations for treasure, 6 of which are unguarded, so fairly small. 10 rooms will have normal treasure for a monster type.
Now, a party consisting of 5 Fighters would need 10,000 XP to go from 1st to 2nd level (My more realistic party mentioned above would need 9,250XP but since XP gets divided evenly, we'll just assume enough for the Fighters to level, and the M-U will just have to stick it out for another session or so on the 2nd dungeon level before going up). That would be 8,000 XP from treasure on the first level.
If I've done the math right, a 1st level unguarded treasure has an average value of only 126GP. There's a minimum of 100SP, and a maximum of 600SP, 60GP, 6 gems worth 1000GP each, 6 pieces of jewelry worth 1800GP each, and a magic item, for a grand total of 16,920XP (and since we're shooting the moon here, throw in a staff of wizardry or a ring of 3 wishes as that 1 magic item). But the odds of that are pretty darn low. No, I'm not gonna calculate it (started to, but getting 600SP and 60GP was just over 1%, and adding 6 gems worth 1000GP each was already about 1 in 200,000). While there's potential for a massive unguarded haul, it's not likely to happen.
With an average of 126GP from unguarded treasure on the 1st level, and 6 of those, that's an average of 756XP from unguarded treasure. That means those 10 monster treasures need to contain a total of 7244GPV/XP. 725GP per monster encounter actually doesn't seem too bad for 1st level dungeons, but this is, as I mentioned above, a 'best case' scenario, where the players manage to find all of the treasure, haul it all out successfully, and not have anyone die in the process.
Of course, most monsters that 1st level characters will fight don't actually have that much treasure, on average. But there are some. Goblin lairs, Giant Rats, Ogres, Owl Bears, Gnomes, Bugbears, and a few others in the Basic Set have treasure type C, which has an average 1000GP. These would be tough fights for 1st level guys, but could be done with planning, smart tactics and some luck.
These numbers work for the 1st and 2nd levels of our fictional dungeon, as characters need the same amount to rise from 2nd to 3rd level, 2000XP for Fighter types, so another 10,000XP all around. I'll need to do some more math for deeper levels, which I'll try to get done tomorrow or Friday my time and post on the blog then.