Oil painting often comes in a high-viscosity form, meaning that it can be quite thick straight from the tube. If you’re looking to avoid the use of paint thinner, you can use colors that are more fluid or you can use water-based oil paints.  You can also use linseed oil instead of mineral spirits to thin your paints. Poppy seed, walnut, and safflower oil are other popular oils that can be used to thin oil paints, but keep in mind that they will extend the drying time.