Headingley is sold-out for the blockbuster Roses match between third-placed Yorkshire and Lancashire, last season's beaten finalists, who lie seventh. In a round replete with England players, Yorkshire possess a squad teeming with international quality after Joe Root and Adam Lyth have been released to join the likes of Jonny Bairstow, Tim Bresnan, Adil Rashid and Glenn Maxwell. Andrew Hodd and Will Rhodes miss out on selection.
Worcestershire add international pairing Moeen Ali and Saeed Ajmal to their squad, with Sachithra Senanayake ending his brief stint at the county. Northamptonshire meanwhile welcome Olly Stone back into the squad after an injury for what will be Shahid Afridi's last match with the county before he departs for the Caribbean Premier League. Both Northamptonshire and Worcestershire have played just two games, with Northamptonshire having lost them both and Worcestershire winning one and losing one.
Leicestershire will be pleased with their start that sees them sitting fourth in the table after four matches but they face a tough challenge away to Nottinghamshire who have added Stuart Broad and Ben Hilfenhaus to an experienced and high-quality squad already boasting Alex Hales, James Taylor and Darren Sammy.
Derbyshire will be looking to build on their impressive victory over Lancashire last week when they host Durham. Durham have named Ben Stokes in their 14-man squad but are without Calum MacLeod who is on national duty and have left out Graham Onions and Barry McCarthy from last week's squad.
High-flying Kent, who have won four from five, host Gloucestershire, who haven't played since Michael Klinger's hundred carried them to victory over Essex in Game Week 2. Kent have added Matt Hunn and Ryan Davies to their squad that beat Somerset and have left out David Griffiths. James Tredwell is still out with injury. Gloucestershire meanwhile haven't included Robbie Montgomery in their squad.
Hampshire moved to second in the South Group with a strong win against Middlesex on Thursday and will take a big stride towards the quarter-finals if they can win a tough fixture away to Somerset. Somerset have added Tom Groenewald to their squad from their thrilling defeat against Kent. All eyes will surely be on Chris Gayle who has plundered 243 runs from his two innings in the T20 Blast this season.
Both these counties have shown glimpses of promise this season but both have been beaten twice and a third defeat could quickly turn a promising start sour. Glamorgan, who have won the last four encounters between the two sides have not yet named their squad. Middlesex, meanwhile, have added Kyle Abbott to the squad that was beaten by Hampshire on Thursday.
Only five matches into the season it is already approaching must-win time for Essex who are at the bottom of the South Groups having lost four matches. Essex have, in fact, lost eight of their last nine matches having won all of the eight preceding that. They face a Surrey side also in need of a win having lost two of their three matches.
Freddie Wilde is a freelance T20 journalist. @fwildecricket