In this work, experimental speed of sound values (U) in the compressed liquid phase of methyl nonafluorobutyl ether and ethyl nonafluorobutyl ether from 283.15 to 323.15 K and for pressures ranging upto 100 MPa are presented. The experimental speed of sound data, together with compressed liquid densities in the range between 0.1 and 40 MPa [Pineiro et al., Int. J. Thermophys. 24 (5) (2003) 1265] were used to estimate densities and isentropic compressibility of both fluids upto 100 MPa. (C) 2004 Elsevier B.V. All rights reserved.