Crosswell two-step migration, VSP-CDP mapping followed by post-map migration, was applied to two complex reservoir data sets collected from JiangHan Oilfield and ShengLi Oilfield in China. The goals of the surveys were to delineate structural and stratigraphic complexities to assist in production and recovery planning for the reservoir. The final migrated images clearly depict the fault structures in JiangHan Oilfield profile and indicate the location and extension patterns of the faults in ShengLi Oilfield. In migrating crosswell seismic reflection data, complications such as edge effects, migration smiling effects, and post- critical reflections, which arc associated with the survey geometry and downhole environment arc often encountered. This two-step migration can reduce these effects. If interpretation is done using both the VSP-CDP mapped image and the post-map migrated image, real geological structures can be distinguished from migration artifacts.