Slow slip events (SSEs) in subduction zones have been observed in the last decade with continuous GPS stations. Some of them could be related to the lateral segmentation of subduction interface that seems to be a critical parameter for the propagation of large subduction earthquakes. In 2006, one of the largest SSEs recorded so far was captured by a dozen continuous GPS stations, in the Guerrero area (Mexico) along the Mexican subduction zone. Previous studies based on these data suggested a lateral variation of the updip depth of the SEE at the Guerrero seismic gap, but suffered from a lack of resolution east of the gap. Here, we show the ability of InSAR technique to capture a part of the 2006 SSE cumulative displacement east of the Guerrero gap by a stacking approach. We processed long strip Envisat interferograms corrected for orbital errors and interseismic signal using GPS data. We first use a forward modelling approach to test InSAR sensitivity to the amount of slip, depth and width of the slipping area on the subduction interface. Due to its high spatial resolution, InSAR allows one to comprehensively sample the North-South spatial wavelength of the SSE deformation, complementing the sparse GPS network. InSAR locates the maximum of uplift and subsidence caused by the SSE more precisely than the GPS data, giving better constraints on the updip slip limit of the SSE. We then inverted the InSAR and GPS data separately to understand how each inversion resolves the slip at depth. Finally, we performed a joint inversion of InSAR and GPS data, which constrained the SSE slip and its location on the plate interface over the entire Guerrero area. The joint inversion shows significant lateral variation of the SSE slip distribution along the trench with a shallower updip edge in the Guerrero seismic gap, west of Acapulco, and a deeper slip edge further east. (C) 2013 Elsevier B.V. All rights reserved.