The solubilization of hydrocarbons by micelles formed of diblock and symmetric triblock copolymers in water are compared in the framework of a mean-field theory of solubilization. The block copolymers contain poly(ethylene oxide) as the hydrophilic block and poly(propylene oxide) as the hydrophobic block and are designated as E(X)P(Y)E(X) or E(W)P(Z) (where E and P denote ethylene and propylene oxides and the subscripts denote the number of segments). In the presence of a variety of aromatic and aliphatic hydrocarbon solubilizates, the core radius, corona thickness, and aggregation number of the micelle and also the volume fraction of the hydrocarbon solubilized in the core are predicted, The calculations show that for identical molecular weights and block. compositions, the diblock (E(200)P(64)) copolymer micelles have a much larger core radius, corona thickness, aggregation number, and volume fraction of the hydrocarbon solubilized in the core compared with the symmetric triblock (E(100)P(64)E(100)) copolymer micelles. In contrast, the diblock copolymer (E(100)P(32)), having the same block composition but half the molecular weight of the symmetric triblock copolymer (E(100)P(64)E(100)), gives rise to micelles having the same core radius, corona thickness, and volume fraction of the hydrocarbon solubilized as the micelles formed of the triblock copolymer, and an aggregation number twice that of the triblock copolymer micelle.