We determine S-wave crustal velocity structure of the Sigsbee abyssal plain in the Gulf of the Mexico, using multicomponent ocean bottom seismometer data. We first construct a 2-D P-wave velocity model by applying a raybased travel-time inversion to the vertical component data. Then, we make an attempt to identify in the radial component records the events associated with P-S mode conversion. Using iterative forward modeling, we constrain S-wave velocities of the layers identified in the P-wave model. We are able to identify the mode-converted events with high confidence, because of the relatively simple geologic structure of the area. Vp/Vs values of the sedimentary layers and their relationship with Vp is indicative of lithologic change with depth: poorly consolidated shale at the top, compacted shale in the middle, and carbonates at the bottom.