Ultrasonic speeds in the liquid phase of 1,1,1-trifluoromethane, CF3CH3, have been measured by a sing- around technique operated at a frequency of 2 MHz. The experimental results mere obtained along eight isotherms from 243 to 333 K at pressures fi om near the saturation line to about 30 MPa. The probable uncertainty in the results was within +/-0.2% in the high-density region. These results are used for comparison with those for other hydrofluorocarbons, and it is found that the absolute values for those substituted decrease in the order CF3CH3 > CF3CH2F > CF3CHF2 over the whale range of conditions, corresponding to the increasing number of fluorine atoms.