Marine controlled-source electromagnetics (CSEM) has grown into a useful method for oil and gas exploration, with many surveys acquired worldwide since 2000 by industry including ExxonMobil. Pre-drill prediction success rates are encouraging. The technology is geophysically sound, but needs more development to be useful across the full Upstream. CSEM data interpretation is improved significantly by integration with other data including seismic. An example from deepwater Brazil shows the ability of CSEM to map facies. Extension of the technology to offshore deepwater Libya poses new challenges, including resistive non-reservoir facies and deep targets.