Cooking spray is a spray form of an oil, combined with lecithin as natural greasing agent, an emulsifier, and a propellant such as food-grade alcohol, nitrous oxide, carbon dioxide or propane. Cooking spray is applied to frying pans and other cookware to prevent food from sticking. Traditionally, cooks used butter, shortening, or oils poured or rubbed on cookware. Most cooking sprays have fewer calories per serving than an application of vegetable oil, because they are applied in a much thinner layer: US regulations allow many to be labelled "zero-calorie"; UK food manufacturer MH Foods have a patented 1 calorie per spray cooking oil. Popular US brands include Pam and Crisco. Sprays are available with plain vegetable oil, butter and olive oil flavor.