Multi-author blogs: sharing revenue?

[KidLifeCrisis]

I'm curious about the topic of having a blog with multiple authors -- probably 3+.

How does revenue sharing work? Does the blog manager typically offer a percentage of the revenue as long as they continue to post X posts/week with Y words/post, or do they get a flat dollar figure per post?

If it's a percentage based share of the revenue, what happens when another blogger is added to the team and you need to offer them a percentage too? I can't see the other authors being okay with a reduction in percentage of revenue share just for a new author to come along and take it.