The diffusion coefficients of p-chloronitrobenzene (p-CNB) in CO2-expanded methanol were measured using the chromatographic peak broadening technique. The measurements were conducted in a temperature range of 323.2-343.2 K, a pressure range of 3.39-10.53 MPa, and a CO2 mole fraction in methanol range of 0-0.5. The diffusion coefficients of p-CNB in the CO2-expanded methanol increased with increasing CO2 mole fraction in methanol at all operational temperatures and pressures. The p-CNB diffusion coefficients were observed to increase with increasing temperature at a fixed pressure for all CO2 mole fractions studied, and decrease with increasing pressure in a fixed temperature and CO2 mole fraction operation. A modified Wilke-Chang equation that could correlate measured diffusion coefficients with an average absolute deviation of 5.68% was proposed in this study. (c) 2008 Elsevier B.V. All rights reserved.