Merc Experience/Baal Runs

[Griselda]

It's not that simple. The Arreat Summit explains things very well on this page.

A monster has a base experience value of X. The formula is:

Experience = X * (n + 1) / 2

n is the number of players in the game. So, you don't get 8x experience, but you get more experience with 8 players in the game.

Here's what they have to say about parties:

Experience In a Party
The total experience earned for killing a monster is increased by 35% when a party member of the killer is in the same named area, defined as the "level" on the Automap. Then the pool is divided as explained below:

The total experience earned for killing a monster is divided evenly among all party members. Each member's share of the experience is equal to the member's level divided by the sum of all members' levels. This Experience Share is then multiplied by another percentage, calculated on a sliding scale that is based on the difference between your character's level and the monster's level, regardless of whether you are in a party or not. The sliding scale only applies if the difference is between 5 and 10 levels. With a small difference (5 levels or less), you receive 100% of your Experience Share. With a large difference (10 levels or more), you will receive 5% of your Experience Share. As a result, high-level characters receive only a small amount of experience for killing low-level monsters. Similarly, low-level characters only get a small amount of experience for killing high-level monsters. This is so that a low-level character running in a high-level party won't receive ridiculous amounts of experience fighting high-level monsters that only his party-mates can destroy.

Finally, only those party members within 2 screens of the monster death receive experience.

I know I've recommended lots of other sites to you, but the Arreat Summit is also a good place to browse if you're wondering how something works.