BEER***

What part of the country do you live in? Will you be serving any other types of alcohol?

It depends on how heavily they drink.

My family is pretty much nothing but alcoholics and I refuse to have a buch of drunks. One keg holds 160 12oz glasses of beer, since our guest list is 200 and a % won`t come, we are getting one keg and a few cases of wine. We are permitted to bring our own alcohol so we are limiting it.
It depends on how much your guest drink and how much you will allow them to drink, as well as what other types of beverages you`ll be having, such as the other posts mentioned.
There will be too many kids at my wedding to have a lot of alochol and the last thing I want is a guest either with a dui or worse.

I would say that with four hours of party time and with your number of guests, I would buy three kegs. That way, it averages to about one drink per hour, per guest. You`ll have guests who drink a few more, and some that will drink a few less. I would imagine it would even out. Good luck!

I second the 3 Keg opinion. If you`re serving wine too... I would go with only 2 Kegs of beer...