According to Official Guinness Records,
The record for the world's largest soda float was one of 13,638 litres (3,000 gal) made by Coca-Cola at the World of Coca-Cola Museum in Atlanta, Georgia, USA, on 25 May 2007.
The float comprised 12,956 litres (2,850 gal) of Vanilla Coke and 7,200 scoops of ice cream, which was pumped into a 15 ft tall glass.
For a complete list of 2007 records, please visit 2007 Guinness Records in United States.