We investigate the impact of over- and under-burden resistivity structure on the time-lapse monitoring of the subsurface reservoirs with CSEM method. We show that even the introduction of a single, thin, high-resistivity layer in the over-burden may effectively remove our monitoring capability. Such a layer even in the under-burden can affect our monitoring capability significantly. In the over-burden the impact of the high-resistivity layer decreases as the high-resistivity layer gets closer to the reservoir, while the opposite is true when the high-resistivity layer is in the under-burden. The effect of the high-resistivity layer is negligible only if located deeper than two times the reservoir burial depth.