Auto GP will merge with the fledgling Formula Acceleration 1 series in a bid to boost grids for both categories in 2015.
Italian-based Auto GP and the FA1 championship organised by Dutch management company ISRA both use the same Lola-Zytec cars that raced in A1GP until the end of the 2008 season.
It is hoped the collaboration between Auto GP promoter Enzo Coloni and Dutch businessman Henk de Jong will guarantee grids of at least 18 cars for next season's Auto GP championship.
Coloni said: "I think this will be a pivotal collaboration and will also guarantee 18 cars on the grid of all the seven Auto GP events we have scheduled for 2015.
"I am sure that, by joining forces, we will be able to achieve considerable success and deliver a really exciting season."
Only four drivers completed a full season of Formula Acceleration in 2014, while grids peaked at 14 cars for the final round at Assen. Auto GP grids were similarly modest.
ISRA president de Jong said both championships had entered into a merger for "the good of the sport".
"More cars, stronger competition, excitement for the spectators and therefore also better for drivers, teams and their sponsors," he said.
2015 AUTO GP CALENDAR
April 19 - Marrakech (WTCC)
May 3 - Hungaroring (WTCC)
May 24 - Silverstone (BLANCPAIN)
June 28 - Paul Ricard (WTCC)
July 12 - Zandvoort (DTM)
September 6 - Brno (ETCC)
TBA - Barcelona
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