Future internal combustion engines demand higher efficiency, progression towards is limited by antiknock quality of present fuels and energy economics in octane enhancement. A possible solution is Octane-on-Demand, that uses a combination of high and low octane fuels in separated tanks to generate fuels of the required octane rating according to demand. Methanol, a RON 109 fuel was selected as the high octane fuel and five low octane fuels were used as base fuel. These were FACE (Fuels for Advanced Combustion Engines) gasolines, more specifically FACE I, J and A and their primary reference fuels (iso-octane/n-heptane). Experiments were conducted with a modified Cooperative Fuel Research (CFR) engine. For SI combustion mode the CFR operated at RON and MON conditions. The engine i.e. also operated in HCCI mode to get the auto ignition properties at lean conditions (λ=3). The engine was then operated under different combinations of engine speed (600,900 rpm) and inlet temperature (52°C and 149°C) to obtain four HCCI numbers. The fuel blends were also tested in an ignition quality tester (IQT) to obtain Blending Derived Cetane numbers (BDCN). The octane numbers corresponding to four HCCI fuel numbers, RON and the MON were obtained for a concentration of methanol of 0, 2, 5 10, 15 and 20%. It was found that the increase of octane number of methanol was not linear with percentage added. The non-linear behavior was described using effective octane number of methanol, or the blending octane number (BON) that changed from close to 200 with a small percentage down to a number closer that of methanol, 109 with larger quantities. The base fuel composition played a significant role for the blending octane number of methanol. Both base fuel octane number and composition mattered.