Phase separation in melts of regular and random multiblock AB copolymers of equimolar composition and various mean block length was modeled using parallel dissipative particle dynamics simulations. Regular copolymers form well-shaped lamellas, strong and super-strong segregation regimes being identified. Microstructure formation in random copolymers with short blocks takes place at higher chi values and results in rough lamellas, the period of which is larger in comparison with the regular multiblocks. For random copolymers, increasing the mean block length deteriorates lamellar morphology and finally results in the formation of a bicontinuous structure. In a large simulation box, multidomain morphologies are observed. (C) 2011 Elsevier B.V. All rights reserved.