Thirty seven soil types from Barbados were analyzed using thermogravimetry (TG) over the temperature range 50-1000 degreesC to determine the associated weight loss. The relative thermal activity "F" of each soil sample correlated significantly with cation exchange capacity (CEC) and clay-related exchange capacity (correlation coefficients ranged from 0.44 to 0.70). The CEC was found to relate to the relative thermal activity through the relationship: F = 1.94 + (0.032 CEC), On the basis of TG, intra-specific variations within soil associations was found to be as significant as inter-specific variations with some of the least as well as the most fertile soils being found among the St. Philip Plain and Grey brown associations. Sugar cane yield per acre for seven consecutive years starting in 1993 was also found to correlate significantly with thermal activity resulting in a linear correlation coefficient of 0.80. On the basis of the above findings "F" is being recommended for determination of the relative fertility levels of the mineral soils of Barbados.