The best way to tell whether a vitamin E oil is pure is to first look at the ingredient list, which should be minimal. Ideally, it should only contain alpha-tocopherol and an oil, like extra virgin olive oil. Additionally, look for vitamin E oils that bear a third-party certification seal whenever possible, such as UL, NSF International, or ConsumerLab, as this verifies that the product contains what it says it does and in the claimed amounts.