The present invention relates to an electronically driven pressure boosting system that is used to boost the torque output of an internal combustion engine (1). The system comprises an electrically driven supercharger (10), an electronically controlled throttle (17) for controlling engine aspiration, and an electronic control system (ECU) (32) for controlling engine operation. The ECU (32) sets the throttle (17) position to regulate the aspiration of the engine (1), and calculates at least one desired aspiration parameter according to engine torque demand (120). The ECU then determines at least one actual aspiration parameter (122,125) according to engine operating conditions (22,25), and compares (63) the desired aspiration parameter(s) (62) with the actual aspiration parameter(s) (122,125). The ECU drives (114) the supercharger (10) to boost aspiration of the engine (1) in accordance with the comparison between the desired aspiration parameter(s) and the actual aspiration parameter(s) only when the torque demand (120) cannot be met by natural aspiration alone.