The perceived intensity and quality of binary mixtures consisting of the common but dissimilar odorants, benzaldehyde (almond), eugenol (cloves), propionic acid (vinegar) and (-)-carvone (spearmint), were determined over a wide range of environmentally relevant concentrations. Consistent data were obtained from each of the odor pairs. This showed that the intensity of odorants not their quality determined the contribution of each to the quality of a mixture. Except for the pair carvone-propionic acid, both odorants were perceived only when the difference between their intensities was small. The results confirmed an earlier finding that the total intensity of a mixture is less than the sum of the intensities of the two components, and also showed that it is never less than the intensity of the weaker component. Seven major characteristics of binary odor mixtures are defined.