This paper presents an experimental study of the Research (RON) and Motor (MON) octane numbers of Liquefied Petroleum Gas (LPG). A comprehensive set of RON and MON data for mixtures of propane, propylene (propene), n-butane and iso-butane are presented, using a method that is consistent with the currently active ASTM Research and Motor test methods for liquid fuels. Empirical models which relate LPG composition to its RON and MON are then developed, such that the simplest relationships between the constituent species' mole fractions and the mixture octane rating are achieved. This is used to determine the degree of non-linearity between the composition and the RON and MON of different LPG mixtures. Finally, implications for LPG fuel quality standards are discussed briefly, as part of a suggested, more substantial undertaking by the community which also revisits the standard test procedures for measuring the RON and MON of LPG. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.