Stricter emissions legislation and growing demands for lower fuel consumption require significant efforts to improve combustion efficiency while satisfying the emission quality demands. Controlled Homogeneous Charge Compression Ignition (HCCI) combined with boosted air systems on gasoline engines provides a particularly promising, yet challenging, approach.Naturally aspirated (NA) HCCI has already shown considerable potential in combustion efficiency gains. Nevertheless, since the volumetric efficiency is limited in the NA HCCI operation range due to the hot residuals required to ignite the mixture and slow down reaction kinetics, only part-load operation is feasible in this combustion mode. Considering the future gasoline engine market with growing potentials identified in downsized gasoline engines, it becomes necessary to investigate the synergies and challenges of controlled, boosted HCCI. Additional HCCI potential can be achieved through the added breathing capabilities, resulting in the extension of the operation map and further optimization of fuel efficiency and emissions (NOx-free, lean operation). These potentials were addressed in this work by thermodynamic analysis of measured data on a 4-cylinder, 2.0L, direct injection, SI engine. This engine was run in HCCI mode up to 6.5 bar BMEP load using a combined boosting system (external boosting and engine turbo-charger). As an outlook, further challenges associated with controlled boosted HCCI were addressed.