The Perfumery Ternary Diagram (PTD (R)) methodology predicts the headspace odor character and intensity of fragrant mixtures, applying the concept of odor value (OV) to multi-component systems. This methodology is extended here to quaternary and quinary odorant systems through the use of tetrahedric diagrams. To present this new methodology, the effect of different base notes in quaternary systems of the type (limonene + geraniol + base note + ethanol) and its forming ternary subsystems has been studied. Base notes selected were: vanillin, tonalide, ambrox, and galaxolide. The Perfumery Quaternary Diagrams (PQD) of the mixtures studied show the different headspace odor character, with ambrox and galaxolide dominating most of the composition spectrum (OVmax). The methodology was also applied to the quinary mixture (limonene + geraniol + vanillin + tonalide + ethanol), and the effect of different concentrations of tonalide on the headspace is presented. V 2009 American Institute of Chemical Engineers AIChE J, 55: 2171-2185, 2009