A fuel's propensity to resist engine knock is described by its Research Octane Number (RON) and Motor Octane Number (MON). Whilst the MON test was originally developed to be more representative of the needs of a modern engine (of the 1930s) recent literature suggests that RON has now become the more appropriate metric to describe the anti-knock performance of fuel, and furthermore that a relaxation in the MON specification could improve vehicle performance, while also helping refiners in the production of gasoline. Previous Concawe work, reported in SAE 2015-01-0767, investigated the effect of RON and MON on the power and acceleration performance of two Euro 4 gasoline passenger cars during an especially-designed acceleration test cycle. A large number of fuels blended with and without oxygenates and ranging from around 95 to 103 RON and octane sensitivities (RON-MON) from 0 to 15 were tested. The results were vehicle dependent, but in general showed that sensitivity and octane index appear to be better predictors for improved acceleration times than either RON or MON alone. In the current study following the initial screening of 4 modern turbocharged, direct-injection vehicles (Euro 5+) on a limited fuel set, 2 vehicles were selected for further evaluation on the full fuel set of 22 fuels, measuring acceleration performance together with efficiency and regulated emissions on the NEDC and WLTP legislative test cycles.