True vapor pressure (TVP) is a common measure of the volatility of petroleum distillate fuels. It is defined as the equilibrium partial pressure exerted by a volatile organic liquid as a function of temperature as determined by the test method ASTM D 2879.
The true vapor pressure (TVP) at 100 ðF differs slightly from the Reid vapor pressure (RVP) (per definition also at 100 ðF), as it excludes dissolved fixed gases such as air. Conversions between the two can be found in AP 42, Fifth Edition, Volume I Chapter 7: Liquid Storage Tanks (p 7.1-54 and onwards)