Ethanol is a promising renewable fuel for spark ignition engine and it can be blended with gasoline in the full range from pure gasoline to 100% ethanol. The objective of this study is to investigate the influence of ethanol content on the research octane number (RON) of a gasoline surrogate. A four-component gasoline surrogate containing iso-octane, n-heptane, toluene and di-iso-butylene is formulated, and the experiments are conducted using seven gasoline surrogate/ethanol blends in a Cooperative Fuel Research (CFR) engine operating according to the standard ASTM D2699. The results of this study show that RON increases with the addition of ethanol, from 89.4 (E0) to 108.6 (E100), but without a linear dependence of RON on the volumetric ethanol content. Moreover, air/fuel ratio and overall burning angle tend to decrease with the increase of ethanol content, while in-cylinder pressure and indicated mean effective pressure are affected positively. The results reported in this study contributes to the acquisition of data for quinary surrogates, since the fuel under investigation is an ethanol-containing four-component gasoline surrogate.