Re: Where does a rocket get the oxygen it needs?

Rockets that use oxygen as their oxidizing agent carry it onboard in the form of liquid oxygen (LOX).  Some rockets use other oxidizing agents such as fluorine or bromine.  These tend to be used on the upper stages of rockets that function outside of the Earths atmosphere, due to their extreme toxicity.  Rockets propelled by solid propellants tend to use such toxic oxidizers as ammonium perchlorate.  [More Info]

For a extensive list of rocket propellants follow this link:  ENCYCLOPEDIA ASTRONAUTICA

-Dennis