Oil paints were used by the old master painters for several hundreds of years.  Even today, it is the most popular of the art mediums for serious painters.  The richness of the paint, depth of color and slow drying time allows artists to blend and rework providing significant flexibility in their creative process.  I started my painting endeavors with oil paints and still use them from time to time.  I do appreciate that they are so forgiving when I am faced with having to make changes and corrections.