Abstract Marine controlled-source electromagnetic (MCSEM) technology has been successfully established as an effective tool for offshore hydrocarbon (HC) exploration. In this paper we consider another application of the MCSEM method for HC reservoir monitoring. We demonstrate that EM methods can be successfully used for the monitoring of production wells in connection with the enhanced recovery of hydrocarbons. We have developed a powerful new EM modeling technique based on the integral equation method with an inhomogeneous background conductivity (IE IBC). This new method, and the corresponding computer software, make it possible to model the EM response over a realistic complex model of a sea-bottom HC reservoir. The numerical modeling results demonstrate that the MCSEM method has the ability to map changes in resistivity caused by the production of hydrocarbons over time. In addition, the EM data help to visualize changes in the location of the oil-water contact within a reservoir. This result opens the possibility for practical application of the EM method in HC reservoir monitoring.