Summary During 2010, PGS conducted one of the first field trials of their towed streamer electromagnetic (EM) system at the Troll field in the Norwegian North Sea. Obviating the need for ocean bottom receivers, the towed-streamer EM system enables CSEM data to be acquired simultaneously with seismic over very large areas in frontier and mature basins for higher production rates and relatively lower cost than conventional CSEM. The towed streamer EM data are currently processed and delivered as a spectrum of frequency-domain responses. In this paper, we review the large-scale 3D inversion of towed streamer EM data using a moving sensitivity domain. We present a case study for the 3D inversion of towed streamer EM data from the Troll field, and demonstrate our ability to image the Troll West Gas Province and Troll East Gas Province.