Abstract: The objectives of the following study were to compare a recently developed low lignin- high fat oat with regular oat as an energy source for use in diets fed to growing-finishing pigs and to compare hammer milling and roller milling as methods of processing oats. A total of 40 crossbred grower pigs (20 barrows and 20 gilts) were assigned to one of five dietary treatments in a factorial design experiment. The control diet was formulated using barley and soybean meal while four experimental diets were formulated in which 40% of either normal or low lignin-high fat oat was substituted for barley. The oats were either ground or rolled. Particle size analysis indicated that the average particle size of the grower diets was 884, 1037, 1420, 1031 and 1501 m while for the finisher diets, the average particle size was 800, 869, 1250, 854 and 1098 m for the barley, ground normal oat, rolled normal oat, ground low lignin-high fat oat and rolled low lignin-high fat oat diets respectively. Digestibility coefficients for pigs fed ground oats were significantly (p<0.05) higher than those for pigs fed rolled oat while there was no difference (p>0.05) in nutrient digestibility between pigs fed normal and low lignin-high fat oat. During the growing period (35.1 to 71.4 kg) as well as over the entire experiment (35.1 to 112.5 kg), there were no differences (p>0.05) in daily gain, feed intake or feed conversion between pigs fed normal or low lignin-high fat oat or between pigs fed ground or rolled oat diets. During the finishing period (71.4 to 112.5 kg), feed intake and feed conversion were poorer (p<0.05) for pigs fed the low lignin-high fat oat compared with the barley diet. There were no differences in carcass traits between pigs fed normal and low lignin-high fat oat or between pigs fed rolled and ground oats. The overall results of this experiment indicate that both normal and low lignin-high fat oat can substitute for barley at levels as high as 40% of the diet without hindering pig performance. Since the average yield of oat can be equal or higher than barley with lower input costs, a re-examination of feeding recommendations regarding oat in swine rations seems warranted. In addition, since pig performance and carcass traits were not affected by processing method and roller mills have been shown to have lower-energy requirements, lower maintenance costs, quieter operation, and more exact control of particle size than hammer mills, there may be some advantage for pig producers to consider roller mills rather than hammer mills for use in processing pig feeds.