We report the critical behavior of osmotic compressibility (chi(T)) that was deduced from turbidity, for two ionic fluid mixtures. The measurements covered the reduced temperature, t, range 7 X 10(-5) less than or equal to t less than or equal to 7 X 10(-2). The mechanism underlying the liquid-liquid phase separation is, predominantly, Coulombic in one case and solvophobic for the other. We find that the criticality of Coulombic phase separation is better described in terms of a crossover from mean field to Ising critical exponents, rather than true mean field exponents, as the critical temperature (T-c) is approached. In addition, we find that the critical phenomenon associated with the solvophobic phase separation in an ionic fluid is characterized by nonclassical critical exponents.