This paper reports comprehensive and accurate measurements of the speed of sound in pure propene in the liquid and supercritical regions. The data have been measured by a double-path-length pulse-echo technique and cover the temperature range from 240 K to 420 K with pressures up to 100 MPa. The measurement uncertainties amount to 3 mK for temperature, 0.01 % for pressures below 10 MPa, 0.005 % for pressures between 10 MPa and 100 MPa, and 0.015 % for speed of sound. The high accuracy of the measurements is demonstrated by comparisons with literature data and three fundamental equations of state.