Coexistence curves for {x(CHCOOC2H5)(2) + (1 - x)CH3(CH2)(4)CH3} have been determined by measurement of refractive index. The critical amplitude B and the critical exponent beta have been deduced from (T, n), (T, x), and (T, phi) (where n, x, and phi are the refractive index, the mole fraction, and the volume fraction, respectively) curves and the value of beta is found to be consistent with theoretical predictions. The experimental results have also been used for the assessment of the Wegner correction terms and the behaviour of the diameter of the coexistence curve in various units over a temperature range of 8 K from the critical temperature. The coexistence curves have been successfully described by combining the Wegner equation and the expression for the diameter.