The surface tension, sigma, of binary mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIm][NTf2] with tetrahydrofuran (oxolane, thf), acetonitrile, dimethylsulfoxide ((methylsufinyl)methane, dmso) and of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [EMIm][NTf2] with dimethylsufoxide was measured between (293.15 and 313.15) K using the pendant drop method. On the basis of experimental sigma values and activity coefficients of solutes in their solutions with ionic liquid obtained from vapor pressure measurement, Gibbs excess surface concentrations of thf, acetonitrile or dmso in mixtures with [BMIm][NTf2] or [EMIm][NTf2] were determined. The results are discussed in terms of possible interactions between ILs and aprotic polar substances. (c) 2013 Elsevier Ltd. All rights reserved.