The density of a typical endothermic hydrocarbon fuel (RP-3) at sub- and supercritical conditions is measured using a novel density measurement method which is based on mass conservation equation and can be applied to the density measurement of single phase flow including supercritical fluids. The measurement covers the temperature range of (295 to 796) K under pressures from (0.1 to 5) MPa. The uncertainty of the measurement is within +/- 0.635 % according to error analysis. The results are fitted as polynomials to analyze deviations. For the 265 experimental data points, the average absolute deviation (AAD) and the maximum absolute deviation (MAD) are 0.539 % and 3.29 %, respectively. In addition, the isobaric thermal expansion alpha(p) is derived from the fitted values of density.