The BSEM (Borehole-to-surface EM) technique is a high precision electromagnetic prospecting method for reservoir boundary delineation. The method can reduce the number of exploration and evaluation wells, provide a reliable basis for the deployment of development wells, and improve the drilling success rate. The method has been successfully applied for more than 10 years in China and become a very attractive technique for the oilfield development process. Field tests and commercial surveys have been carried out in more than 10 oilfields in China, and have achieved very good results.