Blu, no copper wire of the sort used in audio is entirely oxygen free. A minute quantity of oxygen is added in the manufacturing process to chemically bind with impurities and improve the properties of the wire. All the copper wire used in audio applications is better than 99.9% pure. Certain copper used in high temperature hydrogen-rich operating conditions has no oxygen added since it would combine with the hydrogen to form water in a rather undesirable explosive manner, destroying the connection.
Oxygen and moisture in the air, not bound up in the wire, can lead to corrosion. The "oxygen-free" language is fairly standard in today's audio terminology and can be disregarded when buying.
