Abstract: A rotary vane motor uses a gear train arrangement for controlling the position of the vanes as well as the compression ratio of the motor. The motor includes a first pair of vanes namely a leading and trailing vane defining a working chamber therebetween and an opposed second pair of vanes namely a leading and trailing vane defining therebetween a second working chamber. Preferably the motor uses a pair of second order elliptical gears for controlling movement of the vanes to define an intake stage, a compression stage, an expansion stage, and an exhaust stage. In a preferred structure of the motor both the intake port and the exhaust port are movable to change or alter the intake stage and the exhaust stage respectively.