The molar volume, critical micelle concentration, and various acoustic parameters (adiabatic compressibility, intermolecular free length, specific acoustic impedance, molar sound velocity, molar sound compressibility, apparent molar compressibility, relative association, available volume, and solvation number) were evaluated from the density, viscosity, and ultrasonic measurements of the solutions of chromium soaps (myristate, palmitate, and stearate) in a benzene-methanol mixture (4:1 v/v). The molar volumes obtained by using Einstein’s and Vand’s equations showed a decrease with increasing chain length of the soap molecules. The values of the critical micelle concentration obtained from ultrasonic velocity measurements were found to be in close agreement with those evaluated from viscosity measurements and showed a decrease with increasing chain length of the fatty acid constituent of soap molecules.