Oil pastels are crayon-like drawing sticks, where the color pigment is mixed in a wax medium to create a drawing tool. Powder pastels are made by mixing powdered pigment with gum tragacanth and a water/alcohol solution to create a drawing stick.
Soft pastels leave a light, sometimes feathery stroke when applied to paper while oil pastels behave more like a paste or a wax. It is easier to get a stroke of solid color with oil pastels.
Both types of pastels blend easily when applied to paper. Oil pastels have the advantage of being solvent in turpentine while powder pastels are almost always used dry.
A soft pastel drawing needs to be sprayed with a fixative to adhere the medium to the paper while an oil pastel can be left in its natural state as a finished work of art.
There is a subtle difference in color between the two types of drawing tools that is noticeable to the trained eye. Oil pastels tend to have a richer, deeper and more intense color. Powder pastels, however, need to be worked hard into the paper to build up color. This property of the soft powder pastel makes it popular with pleine aire painters and art collectors.
Oil pastels can be applied to other surfaces like masonite or plywood. Powder pastels are always applied to paper, though it is common practice to use many types of colored paper as drawing surfaces, particularly black or gray paper.