According to Official Guinness Records,
The fastest time to run 100 miles on a treadmill by a team of 12 was 8 hr 23 min 00 sec by a team from Radley College (UK) in the Radley College gym in Abingdon, UK, on 13 February 2011. The team members included George Gundle, Hamish Miller, Oscar Richards, Tom Binnie, Archie Hewlett, Hugh Handy, Andrei Ilie, Robin Eliot, Rory Stahelin, Oliver Williams, Charlie Palmer, and Paul Fernandez (all UK).
Gundle, Miller, Richards, and Fernandez each ran 10 miles;Binnie, Hewlett, and Handy ran 9;Ilie, Eliot, and Stahelin completed 7 and Williams and Palmer each ran 6.
For a complete list of 2011 records, please visit 2011 Guinness Records in United Kingdom.