For example, the abundance of oxygen in pure water can be measured in two ways: the "mass fraction" is about 89%, because that is the fraction of water's mass which is oxygen. However, the "mole-fraction" is about 33% because only 1 atom of 3 in water, H2O, is oxygen. As another example, looking at the "mass-fraction" abundance of hydrogen and helium in both the Universe as a whole and in the atmospheres of gas-giant planets such as Jupiter, it is 74% for hydrogen and 23–25% for helium; while the "(atomic) mole-fraction" for hydrogen is 92%, and for helium is 8%, in these environments. Changing the given environment to Jupiter's outer atmosphere, where hydrogen is diatomic while helium is not, changes the "molecular" mole-fraction (fraction of total gas molecules), as well as the fraction of atmosphere by volume, of hydrogen to about 86%, and of helium to 13%.