Increased production of petroleum based products to keep pace with technological advances has taken its toll on the environment. Hydrocarbon contamination of the subsoil and groundwater has become a major problem facing scientists and environmentalists in the 20th century. Initial treatment of contamination sites include the removal of the contaminant from the subsurface for subsequent above ground remediation. Once these methods are exhausted, some type of <i>in-situ</i> remediation, particularly aerobic biodegradation, is sought. Although considered the preferred treatment method, <i>in-situ</i> biodegradation's usefulness is currently limited by oxygen delivery and retention techniques. A novel method of delivering supplemental oxygen to the subsoil, colloidal gas aphrons, has been studied. In addition, this method was compared to the current technique of sparged air injection. The methods and equipment for conducting experimentation on the aeration of an unconfined aquifer, as a vertical slice of soil, have been developed. A specific number of parameters including dissolved oxygen concentration, hydraulic conductivity and tracer dye concentration were measured in order to determine the state of aeration of the saturated soil. Colloidal gas aphrons, CGA, were generated using both NaDBS (sodium dodecylebenzenesulfonate) and Tergitol 15-S-12 surfactants. These dispersions were injected into a 7ft by 7ft by 5in wide two-dimensional vertical slice test cell, which contained about 1600lbs of soil. Continuous dissolved oxygen measurements were conducted using an in-line analysis chamber. Samples were removed through the back of the cell via double-ended shutoff valves and a peristaltic pump. Hydraulic conductivities were monitored to observe variations in fluid flow following the injection of CGA/sparged air. The main conclusions of this work are: l. Both CGA and sparged air introduce dramatic increases in groundwater dissolved oxygen concentrations after injection into the saturated soil. 2. CGA, unlike sparged air/air saturated water, provide supplemental oxygen which forms an "oxygen wall". CGA accumulate near the injection tube forming a stationary front which enhances the dissolved oxygen concentrations of groundwater flowing through the cell. 3. Air sparging does not appear to be as efficient a means of oxygen enhancement of the subsoil as CGA delivery. / Master of Science