Abstract An indirect and extremely precise indicator of sound velocity, triggering frequency, was measured in several fatty acids and triglycerides between 30° and 65 °C. Triggering frequency values, which are readily convertible to velocity values, were obtained after preheating the sample to the desired temperature and then allowing it to equilibrate for about 5 min in a commercial sound velocity analyzer. The calculated sound velocities of several fatty acids and triglycerides increased with either increasing chain length or increasing unsaturation. Adiabatic compressibilities at 40 °C decreased with increasing chain length in the saturated fatty acids, whereas no systematic relationship was observed for tributyrin, tricaproin, and tricaprylin. Relative adiabatic compressibilities at 65 °C for C 18 unsaturated fatty acids decreased progressively from oleic to linolenic acids. The compressibility value at 65 °C of trans elaidic acid was slightly greater than that of the cis isomer, oleic acid. From these data and from idealized crystalline structural drawings, some general conclusions were drawn concerning the conformations and packing of fatty acid molecules in the liquid state. Triggering frequency was also measured in several alcohols, aldehydes, fatty acids and 2-ketones. A linear relationship existed at shorter chain lengths when the log of the number of carbons versus the triggering frequency at 65 °C was plotted. The methylene increment for the fatty acids, calculated from the molar sound velocities at 40 °C, was 190.07.