Development of effective strategies for applying supercritical water oxidation (SCWO) technology to the destruction of hazardous materials requires knowledge of the physical, chemical and transport properties near the critical point. Addition of small amounts of dissolved electrolyte and/or volatile components to water can significantly affect the location of the critical point and, concomitantly, the region of P-T space in which SCWO techniques proceed most efficiently. The Synthetic Fluid Inclusion Technique provides a relatively simple experimental method for determining critical properties of aqueous solutions applicable to SCWO technology. With this technique, samples of the fluid(s) are isolated at elevated temperatures and pressures and maintained for later laboratory study. By observing the behavior of the trapped inclusions during heating in the laboratory, the critical temperature and pressure, the slope of the critical isochore, and the limits of immiscibility are easily determined.