A Transcritical Regenerative Series Two stage Organic Rankine Cycle (TR-STORC) is proposed to improve the efficiency of existing Series Two stage ORC (STORC) architecture by combining supercritical heating in the high pressure (HP) stage and partial evaporation with regeneration in the low pressure (LP) stage. Exhaust gas and jacket water from a stationary IC engine is used as the primary and secondary heat source respectively. Using cyclopentane as working fluid, system exergy performance is analysed for a range of heat source temperatures and for different ratios of heat available between the heat sources. At lower HP evaporator pressures, lower values of vapour outlet temperatures lead to maximum power output. For a wide range of heat ratios and temperatures, TR-STORC delivers improved exergetic performance over STORC and pre-heated ORC. It is the recommended choice for all scenarios of dual source heat recovery. For the engine design point, TR-STORC delivers increased power output by up to16% and 23% than STORC and pre-heated ORC respectively. TR-STORC maintains exergetic superiority for all the working fluids investigated with maximum net power outputs exceeding STORC by15–34% and preheated ORC by 15–52%.