The densities at T = (288.15, 293.15, 298.15, 303.15, and 308.15) K and sound velocities at T = 298.15 K have been measured for aqueous solutions of urea, N-methylurea, N,N'-dimethylurea, N,N,N'N'-tetramethylurea, N-ethylurea, N,N'-diethylurea, 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 and their limiting values are discussed in terms of solute-solvent and solute-solute interactions. (C) 2012 Elsevier Ltd. All rights reserved.