Coal reactivity is an important parameter related to efficiency of boilers, and learning how to predict it can reduce costs when screening for new fuels. We have measured the reactivity of Spanish coals in a high pressure thermogravimetric analyzer, under operational conditions similar to those found in Pressurized-Fluidized-Bed-Combustion (PFBC). The results obtained from non-isothermal tests were used to look for correlations between the reactivity and the physical and chemical properties of the coals. Reactivity increased with increasing rank, but no relationship was found with the initial pore or surface characteristics of either the coals or the chars. We found a correlation between the true density of the chars and their reactivity. We also observed a decrease in the reactivity, calculated from isothermal tests, as the pressure was increased, while there was a slight increase in reactivity with increasing temperature.