I'm getting a 50/50 answer on this one. Some say that oil based primer is for oil paint and latex primer is for latex paint. The reason is that latex is water based, and oil and water do not mix. Eventually what may happen is that the paint will bubbles up because the oil needs to go somewhere. Others say the latex paint can go on top of oil based primer because once the primer dries out, it's not oil based anymore. Both manufacturers Zinsser and Kiltz say that latex paint can go on top of a oil based primer.