Yes, you can paint latex over an oil based paint. It is best if you were to prime the surface first. I wouldn't suggest you using Kilz because it was made to be a spot primer. Usually you would have to put 2 coats to give good coverage. I do recommend Behr primer and paint. It is sold at Home Depot. It was rated #1 in Consumer Reports magazine over Ben. Moore, S.W., and just about every paint that you can think of.