As Ed said, any oils will work, but you want to get good quality ones. You're applying the oils so thinly that good pigments are important. Winsor-Newton & Holbein oils work well. Sometimes a little Extender, or Linseed Oil, helps to thin them. If you live near an art supply store, you'll often find good sales prices on oil paints. The hand-colored work I've posted in the Gallery are a combination of Marshall's, W-N, Holbein, and other quality paints.
Can't wait to see you post some...