Oval courses at Phoenix, Pikes Peak and Fontana, California, are being dropped from the calendar, leaving the IRL with the same number of races as the rival Champ-car series from which it broke away in 1996.
Both series have struggled for sponsor money and spectators since the split.
Indy-car will lose Chevrolet as an IRL enginemaker this year and Toyota has announced plans to depart after 2006, which would leave Honda to go it alone reports lycos.co.uk
The 2006 season will begin on March 26 at Homestead, Florida, and concludes on September 10 at Chicagoland Speedway in Joliet, Illinois.
The IRL's only event outside the US will be staged on April 22 at Twin Ring Motegi in Japan.
