The ultrasonic velocity (nu) studies were carried out at a frequency of 2 MHz (transducer of x-cut quartz crystal) using ultrasonic pulse echo system (model UX4400-M) on cresols in ethyl acetate at constant temperature of 311 K. The values of internal pressure (pi(i)) and molar free volume (V-f) were calculated from measured values of ultrasonic velocity (nu), viscosity (eta) and density (rho). An attempt is made to rationalize the ultrasonic velocity (v), internal pressure (pi(i)) and free volume (V-f) of binary mixtures using Kosower solvent parameter (Z), Dimroth solvent parameter (E-T) and Dielectric constant (is an element of). It is found that there is linear correlation between ultrasonic velocity and acidity constant pk(-1)a, indicating the dependence of acidity. Correlation of Ksower and Dimroth parameters with ultrasonic velocity confirms that solvent polarity is an important factor in the variation of ultrasonic velocity in the present investigation. (C) 2004 Published by Elsevier B.V.