This Demonstration applies a DePriester chart, a set of nomograms to find the vapor-liquid equilibrium ratio (the gas phase mole fraction divided by the liquid phase mole fraction, known as the -value) for a series of hydrocarbons. Select one of three hydrocarbons: methane, propane or -decane. Use sliders to change the pressure and temperature; a green line connects these two points. The green circle indicates where to read the -value on the chart, which is also displayed above the chart. The -values for other hydrocarbons can also be read from the chart.