The Energon Pub

Does anyone know how comic book writers / artists profit from their efforts? Are writers and pencillers given fixed advances for scripts / art pages or do they make money from the profits of the sales? Or both?

Does anyone know how much (roughly) Furman gets paid for one script / issue? How about Roche for his brilliant effort on Kup?

How much do the artists get paid for each issue (or page)?

Just looking for ballpark figures, not exact numbers.

Artists don't get paid much, if at all; from what I've been told, they are contracted and paid for X number of issues OR a series and only get paid when the run is over.
That's just what one guy who worked for Marvel told me.