Thermodynamic properties of fluids are vital information for design, operation and maintenance in the fluid processing or continuous manufacturing industries. Among the thermodynamic properties, some are more important and pervasive with vapor pressure being possibly the most important of all. Practical handling of any fluid requires knowledge of its vapor pressure, and vapor pressure (or boiling point) is invariably among the first properties measured for any substance. These volumes should be of value to professionals in a wide variety of commercial and academic activities because they present vapor pressures for such a wide variety of organic compounds. The present volume IV/20A covers data for hydrocarbons and organic (and some inorganic) chemicals containing S, Se, Te as well as halohydrocarbons, 4252 compounds in total. A general introduction acquaints the the user with the basic concepts and experimental methods of the field.