In this paper, a first step towards a system optimization of organic Rankine cycles (ORCs) is taken by optimizing the cycle parameters together with the configuration of shell-and-tube heat exchangers. In this way every heat exchanger has the optimum allocation of heat-exchanger surface, pressure drop and pinch-point-temperature difference for the given boundary conditions. Different tube configurations are, investigated in this paper. It is concluded that the 30 degrees-tube configurations should be used for the single-phase heat exchangers and the 60 degrees-tube configuration for the two-phase heat exchangers. The performance of subcritical cycles can be strongly improved by adding a second pressure level. Recuperated cycles are only useful when the temperature of the heat source after the ORC should be relatively high. (C) 2014 Elsevier Ltd. All rights reserved.