Abstract The gas resource locked in the thick hydrocarbon-bearing Devonian shales which underlie much of the Eastern U.S. has been estimated to be up to three times the current proven gas reserves of this country. However, the economic feasibility of producing large quantities of gas from this resource remains in question due to the dense structure and low permeability of these shales. Hydraulic fracturing which usually must be employed to stimulate the gas flow involves significant risk of formation damage by the fracture fluids and resultant plugging of gas-flow channels. Thus, basic investigation of the effects of such fluids on the shale structure and properties, having the objective of developing fracture procedures and technology that will avoid the detrimental damage, is needed. This paper describes the methods and presents initial results of a current laboratory investigation of the effects of various fluids such as liquid carbon dioxide, aqueous carbon dioxide, water and proprietary fluids on shale under simulated down-hole conditions. The effects, are evaluated by in situ measurements of permeability, before and after treatment with the fluid, under various applied pressures and pressure differentials. The nature and extent of the "skin effect." are evaluated by examination of the microstructure of the shale. It is expected that the results will provide additional insight into the mechanisms of formation damage and will provide guidance to the design and utilization of commercial fracture technolgoy.