MAYONNAISE Among the vegetable oils used in commercial production of mayonnaise, soybean oil is the major oil used in the United States. Soybean oil is also in Europe a popular basis for mayonnaise as properly refined soybean oil is bland and very stable under the proper processing conditions. Mayonnaise is in most countries legally defined as an emulsified semisolid food with a minimum amount of oil (for example 77 % in France) with egg yolks and vinegar, this in combination with seasonings and several additives.