The melting temperature and heat of fusion were measured for an extensive series of compositionally uniform copolymers of ethylene with butene-1, hexene-1, and octene-1. Fractions and whole polymers that exhibited minimal interchain compositional heterogeneity were from commercial copolymers made with either Ziegler-Natta (ZN) or single-site metallocene catalysts. The present results do not support recent claims that ZN and corresponding metallocene catalyst copolymers melt at significantly different temperatures, nor the implication that comonomer incorporation is "blocky" in ZN copolymers. In five of the six comonomer/catalyst systems the dependencies of the melting temperature on comonomer type and amount were scarcely distinguishable. This common behavior is the same as that for a model random copolymer, so we conclude that most ethylene/alpha-olefin copolymers have random distributions of ethylene sequences. The exception in the present study is a metallocene ethylene/ butene-1 copolymer that melts at lower temperatures and apparently has perceptibly alternating sequence distributions. (C) 2004 Wiley Periodicals, Inc.