This calculation provides a simplified means of estimating Equilibrium Vapour Pressures of various Natural Gas Liquids (NGLs) from the fluid’s Relative Density (60°F/60°F) and Process Temperature.

References
API Manual of Petroleum Measurement Standards Chapter 11 – Physical Properties Data - Section 2 Part 5 – A Simplified Vapour Pressure Correlation for Commercial NGLs, First Edition 2007

ASTM Technical Publication [Stock No. PETROLTBL-TP15]

GPA Technical Publication TP-15