The gaseous PVTx properties of ethyl fluoride (HFC-161)+1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) mixtures were measured at temperatures from 318.180 to 403.205 K and corresponding pressures from 961.3 to 3129.8 kPa using the isochoric method. The uncertainties in the present measurements were estimated to be 1.5 kPa for pressure and 6 mK for temperature. On the basis of the experimental PVTx property data, a truncated virial equation of state was developed for the binary HFC-161/227ea system. This equation reproduced the experimental data in the gas phase within +/- 0.164% in pressure and within 0.178% in density. (c) 2008 Elsevier B.V. All rights reserved.