Painting - latex over oil

I'm getting ready to paint some doors that came out of an old house. I'm not sure, but the paint on them now is probably oil base. Is there an easy way to determine this? Is sanding alone sufficient prep before repainting with latex paint?

Oil has a distinctive look about it and when sanded has an odor that can't be missed. This may not help you. If unsure what may be on the doors, you could paint a small section with latex enamel, let it dry a day and see if it will scrape off easily. If it is oil it will not be hard to remove. Sanding will help overall smoothness but is no assurance latex will bond. An oil based primer would be the way to get a job that will last. Prime, sand lightly with 220 grit remove dust and topcoat....Mike

I would consider using Oil on doors