A comparison of the effect of the process variables temperature and moisture on the extrusion behaviour of wheat starch, whole wheat meal and oat flour was made. The lipids content of wheat starch and whole wheat meal was also adjusted to 4% and 8% using wheat germ oil (WGO) to study its effect and to compare with oat flour, which has an oil level of about 8%. The extruder pressure, torque and specific mechanical energy and extrudate properties of expansion, water absorption index (WAI) and water solubility index (WSI) were analysed. Second-order polynomials were used to model the extruder response and product properties of extruded wheat starch and whole wheat meal with the process variables and WGO level. Wheat starch and meal behaved broadly similarly but differed from oats in pressure, expansion, WSI and WAI in their response to moisture content and temperature. Addition of WGO to wheat starch increased the expansion, whereas it had little effect on the wheat meal. WGO increased the upper bound WSI and decreased the lower bound WAI for starch or meal.