Standard germination and vigor results of 18 cotton seed lots were used to determine seed storability under open storage conditions. Seed moisture content, vigor and standard germination results were checked periodically throughout the experiment. Vigor results were obtained through accelerated aging test, performed after 48, 60, 72, 84 and 96 hours, at 43oC ± 0.5 and l00% relative humidity. Initial germination percentage was effective to predict cotton seed lot storability. Standard germination results remained constant up to 30-month storage period. Regression equations, based either on initial germination percentage or highest single-correlation coefficients obtained for each storage period were developed to estimate seed lot storability.