Coexistence curves for {x(CHCOOC2H5)(2) + (1 -x)CH3(CH2)(9)CH3} have been determined by measurement of the refractive index. The experimental results have been used in the determination of the critical exponent beta, the 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 coexistence curves have been successfully described by a combination of the Wegner equation and the expression for the diameter. The exponents r and b in the relations (1 - phi(c))/phi(c) alpha M-r and B(phi)phi(c)(-1.365) alpha M-b, where phi(c) is the critical volume fraction of (CHCOOC2H5)(2), have been found to be 0.42 +/- 0.01 and 0.28 +/- 0.04, respectively, hence consistent with observations from experimental studies on other chain-molecule solution systems. It supports the Landau-Ginsburg-Wilson type model we proposed recently.