Abstract: An improved rotary engine and method for determining the contours of the sealing surfaces thereof. The improved engine provides for maintaining a predetermined, optimal gap between the sealing surfaces during rotation. The gap may be parallel or angled, and may be positive or negative so as to form an interference engagement. The rotors of the engine may be provided with mirror-image sealing surfaces so as to prevent development of excessive back-lash and clearance, and also to permit efficient reverse operation. The sealing surfaces may also be provided with recesses for interrupting the seal at predetermined points in the rotational cycle, for enhanced wear characteristics and/or to accommodate abrasive or shear-sensitive fluids.