The UK supermarket sector is ominated by Tesco, Asda, Sainsbury's and Morrisons which are the only chains which operate full-scale superstores of 40,000 square feet (3,700 m²) or more. There are no regional supermarket chains left in the United Kingdom which operate superstores, just a few small ones which operate smaller stores. The "Big 4" had a combined share of 75.63% of the UK grocery market in the 12 weeks to 22 April 2007 according to retail analysts TNS Worldpanel.