Controlled-source electromagnetics (CSEM) has been used as a de-risking tool in the hydrocarbon exploration industry. Although there have been successful applications of CSEM, this technique is still not widely used in the industry because the limited types of hydrocarbon reservoirs CSEM can detect. In this paper, we apply the concept of synthetic aperture to CSEM data. Synthetic aperture allows us to design sources with specific radiation patterns for different purposes. The ability to detect reservoirs is dramatically increased after forming an appropriate synthetic aperture antenna. Consequently, the types of hydrocarbon reservoirs that CSEM can detect are significantly extended. Because synthetic apertures are constructed as a data processing step, there is no additional cost for the CSEM acquisition. Synthetic aperture has potential for simplifying and reducing the cost of CSEM acquisition. We show a data example that illustrates the increased sensitivity obtained by applying synthetic aperture CSEM source.