Marine controlled-source electromagnetic (MCSEM) surveys become widely used in off-shore petroleum exploration. However, the interpretation of the MCSEM data is a very challenging problem because of the enormous amount of computations required in the case of the multi-transmitter and multi-receiver data acquisition systems used in these surveys. In this paper we demonstrate that this problem can be solved using the method of electromagnetic migration. We extend the basic principles of electric field migration to the case of joint electric and magnetic field interpretation. The joint migration field is produced by back propagation within the conductive sea-bottom sediments of all electric and magnetic signals recorded in the receivers. We demonstrate that the joint migration of the EM field data provides a better quality image of a sea-bottom resistive structure (e.g., a hydrocarbon reservoir) than the results of individual migration for the different (electric or magnetic) field components.