In this work, measurements of p rho T (pressure-density-temperature) properties of 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone in the near-critical and supercritical regions were carried out. This novel fluid has potential for use in next generation organic Rankine cycle systems because its GWP (global warming potential) is 1. However, there is insufficient data available especially near the critical point. In this work, 155 p rho T data points of 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone along 21 isochores were obtained for densities between 107 and 1526 kg.m(-3), for temperatures ranging from 333.5 to 523.5 K, and at pressures up to 10 MPa. The experimental uncertainties in the measurements of temperatures, pressures, and densities were estimated to be 0.028 K, 4 kPa, and 0.5%, respectively. For densities above 200 kg.m(-3), the uncertainty is 0.4%.