Oil and water are immiscible liquids, which means they do not mix well. This is because oil is a nonpolar molecule, while water is a polar molecule. Nonpolar molecules are molecules that do not have a net electrical charge, while polar molecules are molecules that have a net electrical charge. The polar water molecules are attracted to each other, while the nonpolar oil molecules are attracted to each other. This causes the two liquids to separate into two distinct layers.