Electrical and electromagnetic (EM) techniques are used to map the electrical resistivity of the subsurface. The injection of carbon dioxide (CO2) is likely to form a lenticular, slab or wedge-like bodies of increased resistivity, and therefore resistive thin-layer and sphere models are used for detectability analyses. Thin resistive layer models are used to determine the maximum depth at which resistive layer be detected, and the maximum depth at which time changes in the layer could be monitored. Sphere models are used for quantitatively studying the basic properties of the secondary fields produced on the surface by a finite body at variable depth and in a variety of source fields, and for order-of magnitude rules for depth and size determination of a confined volume filled with CO2. Both surface based EM and DC resistivity methods have limitations for detecting and delineating flat lying resistive features. Configurations with EM sources at depth, which induce vertical currents that are sensitive to the transverse (vertical) resistivity show great promise for detecting and monitoring the emplacement of tabular zones or bodies of resistive CO2.