I have made an effort in the second volume, which addresses the properties and investigations of liquid fuels for combustion engines in the first part and gaseous fuels (excluding solid fuels) in the second part, to present the progress made in this field since the first edition was published. The second volume is also intended for a broader readership and therefore has more of the character of a textbook and reference book in light of this circumstance. For this reason, the table of contents is detailed. Since the octane rating of a fuel is arguably its most important property, this characteristic has been thoroughly discussed, with particular attention given to questions of interest to both mechanical engineers and chemists. In the discussion of octane rating, each aspect was addressed.