In this study, the phenomenon of double retrograde vaporization is explained and experimental data of a binary system showing this type of behavior are presented. In double retrograde vaporization, two 'domes' are observed in the retrograde dew point curve of the P-x-y diagram, instead of the single-domed dew point curve in the familar 'single' retrograde condensation. This results in triple- or quadruple-valued dew points at a specific composition. Double retrograde vaporization occurs within a very limited composition and temperature range very close to the critical point of the more volatile component. Even though double retrograde vaporization has been observed only a few times in literature, we believe that it is the normal behavior and always occurs in binary mixtures in which the two components differ greatly in molecular size. As a case study, experimental bubble point, dew point and critical point temperature and pressure data are presented for the binary system ethane + linalool at five different compositions ranging from 99.79 to 99.98% ethane. The data ranges within temperatures and pressures of 280-350 K and 3-6 MPa, respectively. This system exhibits quadruple-valued dew points at certain concentrations. The results indicate that a very minor change in the concentration can vary the shape of dew point curve significantly. The shapes of the multiple-dew point curves of ethane + linalool are also compared with those of the binary system ethane + limonene. (C) 2002 Published by Elsevier Science B.V.