Because of their wide application within the petroleum industry, it is natural to consider geophysical techniques for monitoring of CO2 movement within hydrocarbon reservoirs, whether the CO2 is introduced for enhanced oil/gas recovery or for geologic sequestration. Among the available approaches to monitoring, seismic methods are by far the most highly developed and applied. Due to cost considerations, less expensive techniques have recently been considered. In this article, the relative merits of gravity and electromagnetic (EM) methods as monitoring tools for geological CO2 sequestration are examined for two synthetic modeling scenarios. The first scenario represents combined CO2 enhanced oil recovery (EOR) and sequestration in a producing oil field, the Schrader Bluff Field on the north slope of Alaska, USA. The second scenario is a simplified model of a brine formation at a depth of 1900 m.