The coupling between GaAs injection lasers and multimode optical fibers using spherical ends on the optical fibers is examined. In particular, the results previously published by Kato are shown to be overly optimistic, although considerable improvement over using a flat‐ended fiber is still predicted. Neglecting reflection losses, we predict maximum coupling efficiencies of the order of 60–70% for our typical double‐heterostructure laser diodes and have experimentally measured 62% in a case for which 60% is expected from the theory.