AbstractCanola oil extracted from seeds with a high‐chlorophyll content can contain chlorophyll derivatives in excess of 30 ppm. When processed, this oil has been observed to be less stable than oil (typically containing 5 to 25 ppm chlorophyll) processed from high‐grade seed. Possible causes for this phenomenon were investigated in this study. The effect of initial pheophytin content was examined by mixing fully saturated oil (tricapryloylglycerol) with increasing amounts of pheophytin and then by subjecting the mixtures to processing conditions. When the processed oils were combined with an unsaturated oil (canola oil), the oxidative stabilities decreased as the pre‐processing content of pheophytin increased. Examination of the effect of increased bleaching to remove excessive levels of pheophytin showed that oil stability decreased with increasing exposure to bleaching clay. Additionally, processing treatments did not remove secondary autoxidation products from oil that was abused prior to processing. Such a finding revealed the importance of initial oil quality on processed oil stability, i.e., the greater abuse of the crude oil (resulting in greater contents of secondary oxidation products), the lower the stability of the processed oil. Finally, previous reports by other researchers of pheophytin's pro‐oxidative effect in oil stored in light were confirmed.