I've been taught you can paint oil based paint over water based paint, but NOT water based over oil based. Can you tell clearly whether it is oil or water base?

I painted over oil base (actually stained and varnished) once, a whole houseful of it, and didn't want to use oil, so "sanded" it with Liquid Sandpaper, then painted, in small batches. What a strong odor though.

My favorite brands of paint are Benjamin Moore and Pratt & Lambert.

The best finishes on trim come from a lot of "elbow grease"!
(I guess that's true of a lot of things however...!)
>>> Get some 220-grit sanding sponges to scuff-sand all trim smooth. ANY run, bump, or wave in the trim will just show through in the new paint! Remove all dust.
>>> Prime with a good primer.
>>> TWO coats of the topcoat, preferably a Satin or Semi-gloss. These resist scuffing better, and clean-up easier.
>>> Don't overbrush! Use a top-quality brush and top-level paint for best flow & leveling properties.
Thanks,
Faron

I think oil based or alkyd paint looks the best on wood trim. Yeah I know what people say that latex paints have improved, not as rubbery looking and more durable than they used to be, etc. etc. And all that may be true but I still think oil paint has the nicest sheen and esthetically just looks better on wood trim. Anyway... I happened to use rustoleum paint on some of my wood trim about 6 yrs ago which still looks very good ( it was the oil based type which is billed as being for metal but it works fine on wood too.) I primed it w/ an oil based primer. The thing about the prep work is absolutely true--might be worth even stripping off the layers if there are many and sand to silky smooth.

What faron said will work well.

Alkyd will not perform as well as Acrylic Latex paints. Alkyd will yellow over time, requiring a repaint long before the acrylic enamel.

I suggest Muralo Satin Flow or BM Satin Impervo Waterborne on trim and doors. Great stuff if you like a porcelain like finish.

Michael

You can use acrylic over oil based primer but if your goin to go to the trouble of using the oil primer you might as well stick with the oil topcoat. If your goin with oil use the benjamin moore alkyd enamel underbody 217-00 if your goin with acrylic use something like muralo universal primer or even 1-2-3 if your gonna sand it because the 1-2-3 dries hard so you can sand it well.