Isothermal (vapour + liquid) equilibrium data for the binary systems of (CO + methyl propionate) and (CO + ethyl propionate) were measured at temperatures of (293.15, 313.15, 333.15, 353.15, and 373.15) K and at elevated pressures up to 10.00 MPa. The measurements were carried out in a cylindrical autoclave with a moveable piston and an observation window. The experimental results were correlated using the Peng-Robinson (PR) equation of state and Peng-Robinson-Stryjek-Vera (PRSV) equation of state with the two-parameter van der Waals II or Panagiotopoulos-Reid mixing rule. The comparisons of the calculation results with experimental values indicate that the PRSV equation of state with van der Waals II mixing rule produced the better correlated results. (C) 2012 Elsevier Ltd. All rights reserved.