A program of research on free-burning wood fires is being conducted by the Forest Service to build up experimental data on the properties of such fires, with the iltimate objective of describing the physical phenomena in terms of fundamental laws. Density was the first wood property investigated. This report gives data on the rate of burning of cribs of five species of wood, each of several density classes. Thermal diffusivity values of the wood were also estimated and correlated with the rate of burning.