Oriented poly vinyl chloride (PVC) is extruded PVC pipe that has subsequent deformation processes performed on it to impose molecular orientation in the critical directions.Oriented PVC is mainly used for water reticulation. It was first commercially made in Australia by Vinidex Tubemakers Pty Ltd in 1984. Because of its recent development there has been little published research into the properties of oriented PVC.Research that has been conducted has shown some interesting behaviour in the material. One of those was the tendency for a radial crack, propagating in the radial direction, to change direction and align itself in the hoop (or circumferential) direction. This suggests that energy required to propagate a crack in the hoop direction is less than in the radial direction.This thesis attempts to measure the mode II strain energy release rate (GIIc) in oriented PVC using the popular end notch flexure testing geometry.Once linear elastic behaviour was verified and an acceptable method for finding the instant at which crack propagation occurred in the ENF specimens a range for the GIIc was attained. The range was 0.5 to 1.5 kJ/m2. This is a reasonable value that is below reported mode I delamination values (which are inherently less than the radial Gc values). This explains why a radial crack aligns in the hoop direction.A mechanism for the crack propagation was also developed using micrographs of mode II propagated crack tip surfaces. The micrographs showed three distinct stages in the development of a mode II crack in an ENF specimen. This mechanism helped to explain the scatter in the results as well as the observed behaviour of the crack tip during testing.