Fuel efficiency and emission performance sensitivity to fuel reactivity was examined in a fuels assessment of Delphi’s second generation Gasoline Direct-Injection Compression Ignition (GDCI) multi-cylinder engine. The study was designed to compare a US market gasoline (RON 91 E10) to a higher reactivity gasoline (RON 80) at four operating conditions ranging from light load of 800 rpm, 2 bar gross indicated mean effective pressure (IMEP) to medium load of 2000 rpm, 10 bar IMEP. The experimental assessment indicated that both gasolines could achieve the performance and Tier 3 emission targets at each of the four operating conditions. Relative to the RON 91 E10 gasoline, the engine performance benefits associated with the RON 80 gasoline were consistent with our previously reported single-cylinder engine research . More specifically, a significant fuel consumption improvement was observed at the low load operating conditions (800 rpm, 2 bar IMEP and 2000 rpm, 2.6 bar IMEP) when using the RON 80 gasoline, compared to using market RON 91 E10 gasoline mainly due to its higher reactivity. During mid-load operation (1500 rpm, 6 bar IMEP and 2000 rpm, 10 bar IMEP), significantly lower fuel consumption was achieved when using the RON 80 gasoline due to better combustion as well as lower boost pressure requirements. Clear differences in low temperature heat release (LTHR) behavior for this partially premixed compression ignition (PPCI) combustion process was also observed among the two gasolines. From these data, we conclude that the fuel consumption and emission targets for Delphi’s second generation GDCI engine were reached when using RON 91 E10 US market gasoline with further potential to improve light-load combustion behavior and to reduce fuel consumption through optimization of the fuel.