Oxygen is composed of three isotopes: oxygen-16, oxygen-17 and oxygen-18 and has an average atomic mass of 15.9980 amu. Oxygen-17 has a mass of 16.992 amu and makes up 0.035% of oxygen. Oxygen-16 has a mass of 15.982 amu and Oxygen-18 has a mass of 17.984 amu.
