Oxygen Oxygen is an element that is in the air and water all around us. It is also the gas that we breath. Joseph Priestly and Carl Whelm Scheele both discovered oxygen but it was Priestly Who was mostly given the credit for the discovery. They were able to produce oxygen by heating mercuric oxide. Priestly called the gas he had produced dephlogisticated air‘ during his experiments ‘dephlogisticated air' and Carl Scheele called the gas he had produced during his experiments ‘fire air’.