We report viscosities of liquid hexadecane measured at temperatures between (323 and 673) K and at pressures up to 4.0 MPa. This study significantly extends the temperature range over which viscosity data for hexadecane are available. The experiments were carried out using a dual-capillary viscometer that measures the ratio of the viscosity at the temperature in question to that at a reference temperature, 298.15 K in this work, at which the viscosity is well known. Absolute viscosities were then obtained with an estimated expanded relative uncertainty of about 3 % at 95 % confidence. An empirical function was developed to correlate the viscosity ratio with the density ratio and this fitted the experimental data within about 1 %. The results were found to agree well with the existing literature data.