An oil's a substance that's in a viscous liquid state ("oily") at ambient temperatures or slightly warmer, and's both hydrophobic (immiscible with water) and lipophilic (miscible with other oils, literally). This general definition includes compound classes with otherwise unrelated chemical structures, properties, and uses, including vegetable oils, petrochemical oils, and volatile essential oils. Oil's a nonpolar substance. The term oil's often used colloquially to refer to petroleum. Types o… (More on Oils)