Osmotic coefficients of the solutions of room temperature ionic liquid N-R-4-(N,N-dimethylamino)pyridinium tetrafluoroborate (R = C4H9, C5H11, C6H13) in ethanol have been measured at T = 298.15 K by the isopiestic method. The experimental osmotic coefficients have been correlated using the ion interaction model of Pitzer, electrolyte non-random two liquid (e-NRTL) model of Chen, non-random factor (NRF) and a fourth-order polynomial in terms of molality. The vapour pressures of the solutions studied have been evaluated from the osmotic coefficients. (C) 2012 Elsevier Ltd. All rights reserved.