SUM and SQL

[PJB]

How come this gives me the right sum

sqlstring = "Select SUM([GEService].[PayAmount]) AS [GEAmount] From GEService"

But this

sqlstring = "Select SUM([GEService].[PayAmount]) AS [GEAmount], SUM([WSService].[PayAmount]) AS [WSAmount] From GEService, WSService"

returns the 2 seperate amounts the way i'd like it to but the are exactly 3X and 4X (respectively) the amount they should be?