(Liquid + liquid) coexistence curve, turbidity, and isobaric heat capacity per unit volume for the critical solution of {benzonitrile + n-undecane} have been measured. The critical exponents beta, nu, gamma, and alpha have been deduced, which were found to be consistent with the theoretic predictions. Meanwhile, the experimental data have also been analyzed to obtain the system-dependent critical amplitudes B, xi(0), chi(0), A(+/-), and D corresponding to the difference of the general density variable of two coexisting phases Delta rho, the correlation length xi, the osmotic compressibility chi, the isobaric heat capacity per unit volume CpV-1, and the first term of correction-to-scaling for the isobaric heat capacity per unit volume, which were used to test some universal ratios. It was found that the coexistence curve may be well described by the crossover model proposed by Gutkowski et al. The critical-fluctuation induced contribution to the background heat capacity B-cr was obtained and used to analyze the asymmetric behavior of the diameter of the coexistence curve. The result indicated that the asymmetry of the coexistence curve can be well described by the complete scaling theory proposed by Anisimov et al., and the heat capacity does make a significant contribution to this asymmetric behavior. (C) 2012 Elsevier Ltd. All rights reserved.