Abstract: One form of a retention system includes a pair of aft segments of 180.degree. in length disposed in annular grooves about a compressor spool, the segments having radial projections against which the aft end faces of the base portions of rotor blades abut. The blade base portions are shaped and are received in complementary-shaped slots of the spool. The forward retention system includes a plurality of arcuate segments approximately 30.degree. in length disposed in grooves adjacent the forward end faces of the blades. With the exception of the final pair of blades, the blade base portions thereof are located in the axial complementary slots in pairs, with each forward arcuate segment, except the final segment, being disposed in the groove at a circumferentially spaced location and displaced circumferentially to abut the forward end faces. The final arcuate segment is radially reduced and disposed in the remaining portion of the groove to lie flush with the spool.