Oils are tested by manufacturers for quality control and for fitting the requirements for exporting to other countries. There are general requirements for all edible fats and oils and specific one for each kind of oil. Olive oil is the oil with stricter requirements as it is an more expensive oil which adulteration is more common, more tests are needed to identify quality of oil and sure it is not mixed with other oil. However, consumers are not chemists, so what can we do to judge an oil's quality？