Marine controlled-source electromagnetic (CSEM) surveys have recently found wide application for mapping resistive hydrocarbon reservoirs (Ellingsrud et al., 2002). Typically, these surveys have been target oriented and have been used to delineate potential reservoirs already mapped by other methods. However, CSEM surveys can also be used for reconnaissance in areas where no specific targets have been identified (Srnka et al., 2005). The objective of a reconnaissance CSEM survey is to detect the presence of resistive bodies that are large enough to be economic hydrocarbon reservoirs. These bodies would then be candidates for more detailed seismic or CSEM surveys.