The following season (1948-1949), with a 16-game schedule, the new lineup was league champion Bartlesville Phillips 66ers (15-1 record), Denver Chevvies, Peoria Caterpillars, Akron Goodyears/Akron Goodyear Wingfoots, and Milwaukee Allen-Bradleys.

The league expanded again in the 1950–51 season to eight teams, adding the (Oakland Blue 'n Gold Atlas) and San Francisco Stewart Chevrolets.

The next season (1952-1953), the league dropped down to nine teams, but saw new opponents in the Houston Ada Oilers and the Los Angeles Kirby's Shoes.

Top college graduates increasingly gravitated to the NBA, and the NIBL began to decline in popularity and profitability.

In the NIBL's final season, 1960–61, the league had dropped down to only six members divided into two divisions, Eastern (Cleveland Pipers, Akron Goodyears, New York Tuck Tapers) and Western (Denver-Chicago Truckers, Phillips 66ers, and Seattle Buchan Bakers).

Most of players wanted no part of the uncertain professional game, and instead were accepting a position with the companies, rejecting offers even from NBA.

The NIBL was dedicated to remaining amateur at a time when basketball was desperately trying to carve out some postwar space in the pro sports landscape.

But professional basketball staggered forward and the NIBL flourished, mostly because its stability allowed companies to poach stars such as Bob Kurland.