What is pure oxygen (gas) density as a function of T or P?
A colleague showed me a website that can render almost any thermodynamic quantity as a function of another for various substances: http://webbook.nist.gov/chemistry/fluid/.

Using NIST's software allowed me to get an isobar graph of $\rho (T)$ from 55K to 1000K (at 1.0atm).



And $\rho (P)$ from 0 - 800atm (at 273.15K):


It even has an HTML data-point option (and downloadable tab-delimited form). Perfect! In the case of $\ce{O2}$ it uses data from papers in the '80s and '90s (experimental and (from the software) empirical)