I started with a oil pastel spot using black, gray, and white, and made it into a brush. While it doesn't render a thick oil pastel look, it does look like oil pastels that have been thinned down with oil.

The effect changes with the brush size. For a sharper line, make it smaller. For more texture make it bigger. It has corrective smoothing and stabilization. This image was drawn using this brush.

Examples of lines drawn: