The Bell-shaped or Contour nozzle is probably the most commonly used shaped rocket engine nozzle. It has a high angle expansion section (20 to 50 degrees) right behind the nozzle throat; this is followed by a gradual reversal of nozzle contour slope so that the nozzle exit the divergence angle is small, usually less than a 10 degree half angle. The most important design issue is to contour the nozzle to avoid oblique shocks and maximize performance.