Abstract: An improved hydraulic motor for downhole oil and gas wells to drive a sidewall core cutting apparatus comprising; a motor housing having a fluid inlet channel and a fluid outlet channel directed essentially parallel to each other and tangentially intersecting a rotor cavity with the motor housing containing an eccentrically positioned rotor with radially movable vanes within the rotor in a manner such that the fluid flow enters the cavity essentially tangentially and flows around the rotor and exits tangentially on the other side of the cavity. Such a hydraulic motor exhibits significant improvement in torque and power output at a given hydraulic power input when compared to previous hydraulic motors employed in such applications.