New experimental data for the thermal conductivity of 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone (Novec 649) are reported for vapor, liquid, and supercritical states. These new experimental data were obtained with a transient hot-wire apparatus over the temperature range from 183 to 501 K and at pressures from 0.02 to 69 MPa. These data were used to develop a wide-range correlation for the thermal conductivity of the vapor, liquid, and supercritical fluid. The experimental data reported here have an uncertainty of 1% for the liquid and supercritical regions (densities >600 kg.m(-3)), 1.5% for vapor and supercritical regions (pressures >= 1 MPa and densities <200 kg.m(-3)), 3% for supercritical states (200 kg.m(-3) <= densities <= 600 kg.m(-3)), and 3% for vapor and supercritical states (pressures <1 MPa). The thermal-conductivity correlation developed in this work is estimated to have an expanded relative uncertainty, at a 95% confidence level, ranging from approximately 1 to 4% that depends upon the temperature and pressure, with larger uncertainties in the critical region.