a thermal oil recovery process is disclosed for use in a heavy oil reservoir having a plurality of laterally separated , generally vertical wells whose use have left the reservoir characterized by a heated depletion zone , a channel , voidage , or mobility and communication . the process includes the steps of : drilling a well having a horizontal section and an opening therein that is located laterally between at least two of the vertical wells and at a depth within the lower part of the reservoir ; injecting a steam through the two vertical wells to establish thermal communication with said horizontal well ; and using the combination of steam drive and gravity drainage to recover oil from the reservoir through the horizontal well .