The perturbed-chain SAFT equation of state is extended to heterosegmented molecules and is applied to copolymers with a well-defined (alternating) repeat-unit sequence as well as to systems with a statistical sequence of the monomers in the backbone. Copolymers with a statistical sequence of the constituting repeat units usually require an assumption on the sequence of neighboring repeat units within the chain. A simple approach for defining such repeat-unit arrangements is proposed. Systems containing polyolefine copolymers (poly(ethylene-co-propylene) and poly(ethylene-co-1-butene)) covering the complete range of copolymer composition (including both of the appropriate homopolymers) were modeled in a mixture with solvents. Good results were found for mixtures of copolymer/solvent systems using constant interaction parameters. Copolymers comprising both nonpolar and polar repeat units, for example, poly(ethylene-co-vinyl acetate) and poly(ethylene-co-methyl acrylate), require an interaction parameter correcting the interactions between repeat units of different types, which depends on the repeat-unit composition.