A beautiful medium that exhibits a glow and depth in a finished piece that is not easily achieved with other mediums. Oil does require more consideration and knowledge about the preparation of a good stable and archival surface beforehand. I rarely work in oil but my past pieces were all completed on primed hardboard, mainly in Winsor & Newton artist grade pigments, and a small amount of mineral spirits as the vehicle.
Oil paints I used with small amounts of mineral spirits as a vehicle and worked in a mix of glazing and almost opaque brush stroke lay in method. However, oils may be used, and are used by many artists, successfully, just from the tube, they do not necessarily require any use of thinners. Safety considerations must be taken with oil painting, when using any type of thinners, more so than with watercolour or acrylics.