Instead of the usual single-domed retrograde dew point curves, S-shaped dew point loci may occur in the isothermal pressure-composition diagram of the binary system methane+butane. This phenomenon has the consequence that at and immediately below the critical temperature of methane, isotherms are present showing triple-valued dew points for a fixed concentration. A similar behavior was observed in the binary system methane + pentane. However, in the latter system, in a narrow concentration range at temperatures slightly above the critical temperature of methane, isotherms were determined experimentally showing even two domes in the dew point loci, indicating quadruple-valued dew points at a given concentration. The latter behavior leads to the phenomenon of double retrograde vaporization, i.e. in a pressure-composition diagram at a fixed value of the concentration, the following sequence of phase transitions occur when going from low to high pressures: gas --> liquid + gas --> gas liquid + gas --> fluid. This paper presents bubble, dew and critical point data for the binary system ethane + limonene at five different compositions ranging from 99.50 to 99.93 mol% ethane. The data range within temperatures and pressures of 280-330 K and 3-6 MPa, respectively. This system also exhibits triple- and quadruple-valued dew points at certain concentrations, i.e. this binary system also shows the phenomenon of double retrograde vaporization. The results indicate that a very minor change in the concentration can vary the shape of dew point curve significantly.