Diet Pepsi is a no-calorie carbonated cola soft drink produced by PepsiCo, introduced in 1964 as a variant of Pepsi-Cola with no sugar. First test marketed in 1963 under the name Patio Diet Cola, it was re-branded as Diet Pepsi the following year, becoming the first diet cola to be distributed on a national scale in the United States. In the 1960s and 1970s its competition consisted of Tab, produced by The Coca-Cola Company, and Diet Rite soda, produced by Royal Crown. Diet Coke was a later entrant to the diet cola market; though shortly after entering production in 1982 it became the primary competing diet cola to Diet Pepsi. While the U.S. represents the largest single market for Diet Pepsi, it was launched in the U.K. in 1983 and has since become available on a global scale. The beverage composition, flavor variations and packaging varies based on the country of production.