In a difficult group Durham will have face holders Surrey, runners up Somerset, Nottinghamshire, Hampshire, Welsh Dragons (Glamorgan) and Scotland.
Teams will play every other side in their group home and away. The winners of each group and the best second-placed team will qualify for the semi-finals.
2012 Clydesdale Bank 40 draw
Netherlands
Leicestershire Foxes
Worcestershire Royals
Lancashire Lightning
Middlesex Panthers
Essex Eagles
Gloucestershire Gladiators
Scotland
Durham Dynamos
Hampshire Royals
Surrey Lions
Welsh Dragons (Glamorgan)
Somerset
Notts Outlaws
Unicorns
Derbyshire Falcons
Yorkshire Carnegie
Kent Spitfires
Warwickshire Bears
Sussex Sharks
Northamptonshire Steelbacks