There are qualities that oils used in deep fat fryers should possess that are somewhat different than oils used in other types of cooking. Generally, any oil should be high in monounsaturated fats. Another is a consideration of the higher than normal temperatures used in such cooking. So, probably high on the list would be a good grade of olive oil. Problem is, oilive oil is fairly expensive and has a somewhat lower smoking temperature than others. Another is flaxseed oil, but it's expensive and hard to come by in larger volmes, at least here in the U.S. I'd recommend peanut oil. It has a high smoke temperature, high in the healthy stuff and is reasonable in cost. Additionally, my experience has been that peanut oil doesn't retain the "flavor" of the previously cooked food as does others, especially Canola and some other vegetable oils...