Notts Outlaws and The Blaze will each compete in a 12-game Vitality Blast group stage next summer, after format changes were confirmed.
The Blaze will also compete in 16 group-stage fixtures in the Metro Bank One Day Cup, with the overall volume of women's white-ball cricket in the group stages remaining unchanged.
Notts will be part of a six-team T20 group, alongside Derbyshire, Leicestershire, Yorkshire, Lancashire and Durham, and will play each side home and away. They will play two further group-stage matches against teams from other groups. The knockout stages and Finals Day will be completed before The Hundred.
Vitality Blast women's Finals Day, meanwhile, will now feature two semi-finals and the showpiece final.
Vitality Blast men’s competition
Groups
Group A: Derbyshire Falcons, Durham, Lancashire Lightning, Leicestershire Foxes, Notts Outlaws, Yorkshire.
Group B: Bears, Glamorgan, Gloucestershire, Northamptonshire Steelbacks, Somerset, Worcestershire Rapids.
Group C: Essex, Hampshire Hawks, Kent Spitfires, Middlesex, Surrey, Sussex Sharks.
Group-stage matches
Each county will play the other counties in their group on a home-and-away basis – a total of 10 matches. They will additionally play one home game against a county from outside their group and one away game against a county from outside their group.
This will allow counties to play against all 18 counties, over time, on a rolling basis during the group stage of the competition.
Knockout stage
The top two teams in each group plus the best two third-placed teams will progress to the quarter-finals. The winners of the quarter-finals will progress to men’s Vitality Blast Finals Day.
Vitality Blast women’s competition (Tier 1)
Group
Bears, Durham, Essex, Hampshire Hawks, Lancashire Thunder, Somerset, Surrey, The Blaze, Yorkshire.
Group-stage matches
Each county will play 12 group-stage matches – six home and six away. They will play four counties twice and four counties once.
Knockout stage
The top four counties at the end of the group stage will progress to women’s Vitality Blast Finals Day, which will include two semi-finals and the Final.
Metro Bank One-Day Cup women’s competition (Tier 1)
Group
Bears, Durham, Essex, Hampshire Hawks, Lancashire Thunder, Somerset, Surrey, The Blaze, Yorkshire.
Group-stage matches
Each county will play 16 group-stage matches – each county plays each other county at home and away.
Knockout stage
The top three counties at the end of the group stage will progress to the knockouts stages. The top county progresses straight into the final to meet the winner of the Eliminator between 2nd and 3rd place.