Hampshire, who play Surrey at the Kia Oval tomorrow, moved to the summit on net run-rate with a narrow victory over Glamorgan on Wednesday night.
But the Eagles, with a game in hand on the leaders, travel to Taunton in high spirits after four consecutive triumphs.
Tim Phillips was the hero last week, smashing at unbeaten 33 from 13 balls to lead his side to victory over bottom-side Middlesex Panthers.
In Ravi Bopara, the Eagles have a batsman in the form of his career. The England all-rounder has struck 217 runs in just five matches and is Essex’s key man in the middle order.
However, Somerset boast the leading run-scorer in the competition to date in Craig Kieswetter.
The wicketkeeper-batsman is sitting pretty at the top of the charts with 358 runs from seven games and, opening the innings, is vital to Somerset’s hopes of building a platform for a commanding total on home soil.
Skipper Marcus Trescothick returned from a groin problem to play in Somerset’s LV= County Championship defeat to Nottinghamshire at Trent Bridge and is likely to continue.
* Essex Eagles have won the toss in all five of their Twenty20 fixtures against Somerset, winning twice and losing three times.
* Jesse Ryder has hit 79% of his T20 runs this season in boundaries, the highest percentage of anyone facing at least 50 balls.
* Alfonso Thomas needs four wickets to become the third player to take 100 wickets in English domestic Twenty20 cricket.