At this temperature and pressure Oxygen can pretty much be taken as an ideal gas. I suppose it all depends on what you are trying to calculate and how accurate you want to be.
I have written a units conversion program called Uconeer (which is freeware) that will estimate the compressibilty of several common gases using Peng-Robinson. This is often accurate enough for day-to-day calcs like pipe sizing. You can download the program for free from
This will calculate the density of your gas at the stated temperature and pressure, and you can back-calculate the compressibility from that if you need it.