Is there oxygen on Mars?

There is a small amount of gaseous oxygen in the atmosphere of Mars, about 0.13%. Most of the oxygen in the atmosphere is there as carbon dioxide, CO2. This gas makes up 95% of the very, very thin atmosphere.

However, there is still quite a lot more oxygen on Mars - as iron oxides. These are mostly what give Mars its red color. It would be theoretically possible to extract both pure oxygen and pure iron from these rocks, which is probably where the oxygen for any Mars colonists would need to come from.