Coexistence curves for binary liquid mixtures of {x(CHCOOC2H5)(2) + (1-x)CH3(CH2)(8)CH3} have been determined by measurement of the refractive index. The experimental results have been used in the determination of the critical exponent beta and critical amplitude B, and the study of the diameters of the coexistence curves. The values of the critical exponent beta are found to be consistent with theoretical predictions. The experimental results have also been used in the assessment of the Wegner correction terms over a temperature range of about 11 K from the critical temperature. The coexistence curves have been successfully described by a combination of the Wegner equation and the expression for the diameter. (C) 1998 Academic Press.