The Friends Provident t20 will be reduced from the 2012 season as part of a new structure for domestic cricket.
The pool stage is to be cut from 16 games per team to 10, with eight teams then advancing to the quarter-finals.
The County Championship is to remain unchanged in two divisions of nine teams, with each playing 16 games.
The Clydesdale Bank 40 will be reviewed independently before an England and Wales Cricket Board meeting in May and could be reduced to 20 teams.
The CB 40 currently consists of 21 teams - the 18 counties plus Unicorns, Scotland and the Netherlands - playing in three groups of seven, with four teams advancing to the semi-finals.
The 20-team format would see the competition split into five pools, leading to an additional quarter-final round.
The independent review comes after concerns were raised about the potential lack of guaranteed one-day cricket in August and September.