The densities and sound velocities at T = (288.15, 293.15, 298.15, 303.15 and 308.15) K have been measured for aqueous solutions of urea, N,N-dimethylurea, N,N-diethylurea, N-propylurea, N-butylurea. From these data the apparent molar volumes, V-Phi, the apparent molar isentropic compressions, K-S,K-Phi, and the Passynski solvation numbers of solutes have been determined. The concentration dependencies of the calculated quantities, their limiting values and temperature characteristics are discussed in terms of (solute + solvent) and (solute + solute) interactions. (C) 2014 Elsevier Ltd. All rights reserved.