All training sets considered here are composed of only alcohols, esters, ethers, ketones, acids and alkanes that have ample density and enthalpic data available, and contain only data points measured at nearambient conditions (288.15-323.15K, 0.95-1.05 atm). This set of moieties, containing only carbons, hydrogens and oxygens, was chosen to limit the scope of the study and focus specifically on the choice of training data for a set of molecules. The molecules included exercise a total of 9 LJ types, of which 6 are optimized, shown in Table . A table showing which LJ types are exercised by each molecule in the training set is available in Supporting Information Section 2.1. The three parameters included that are not optimized are all hydrogen parameters; an explanation of why they are not optimized is given in the "Parameters optimized" section.