We have extracted cross virial coefficients between 188 and 480 K for the system nitrogen + oxygen from existing PVT data for air. These values agree with literature values within experimental error. We have also extracted cross virial coefficients for the system water + oxygen from cross virial coefficients of moist air. Our calculations cover the temperature range from 298 to 373 K, but no previous values exist with which to compare. These values, extracted from experimental PVT data, extend or provide cross virial coefficients at conditions for which no previous values have been reported for nitrogen + oxygen and for water + oxygen. The extraction process is the normal procedure for recovering virial coefficients from experimental data.