Simple surrogate formulations for gasoline are useful for modelling purposes and for comparing experimental results using a carefully designed fuel. The most common approach is to start with Primary Reference Fuels (PRF)—i.e., isooctane and n-heptane. These have the disadvantage that they cannot replicate the octane sensitivity (RON-MON) of a real fuel, and so it is common to add toluene to make a Toluene Primary Reference Fuel (TPRF) surrogate. The vapour pressure of TPRFs is much lower than a real fuel, and so the flash boiling behaviour of a real fuel cannot be properly replicated. To overcome the volatility challenges, an alternative to TPRF is advocated which involves replacing some or all the isooctane by isopentane. In the event of total replacement, a three-component “THIP” (Toluene, n-Heptane, Iso-Pentane) surrogate fuel is produced. It is shown that by adding isopentane it is possible to have a simple surrogate that can reproduce the lower part of the distillation curve of a real fuel. Explicit equations are presented that allow THIP surrogates to be created based on a desired RON, MON and DVPE (Research Octane Number, Motor Octane Number, Dry Vapour Pressure Equivalent).