Measurements of the coexistence curves for phase-separated polymer solutions of polymethylmethacrylate in 3-octanone (PMMA/S-OCT) for six different molecular weights of PMMA have been carried out. We have tested the scaling behavior of the order parameter Delta phi (the difference between polymer volume fractions in the two coexisting phases) for its dependence on the degree of polymerization N of the polymer chains and the reduced temperature epsilon=(T-c-T)/T-c. The experiments reveal that, in the asymptotic regime, the measured order parameter has power-law dependence on both N and epsilon, i.e., Delta phi=3.8N(-0.21)epsilon(0.34). Furthermore, when the symmerization procedure of Sanchez [J. Appl. Phys. 58, 2871 (1985)] is used to analyze the data, it suggests that epsilon N-0.46 may be used as a scaling variable for phase separated polymer solutions.