1.1 This standard is concerned with the determination of the vapor pressure (see Note 1) of gasoline, volatile crude oil and other volatile petroleum products. Procedure A is applicable to gasoline and other petroleum products with a vapor pressure of less than 180 kPa. Procedure B may also be applicable to these other materials, but only gasoline was included in the interlaboratory test program to determine the precision of this test method. Neither procedure is applicable to liquefied petroleum gases or fuels containing oxygenated compounds other than methyl t-butyl ether (MTBE). Procedure C is for materials with a vapor pressure of greater than 180 kPa and Procedure D aviation gasoline with a vapor pressure of approximately 50 kPa. Note(1): Because the external atmospheric pressure is counteracted by the atmospheric pressure initially present in the vapor chamber, the Reid vapor pressure is an absolute pressure at 37.8oC in kilopascals. The Reid vapor pressure differs from the true vapor pressure of the sample due to some small sample’s vaporization and the presence of water vapor and air in the confined space. Note (2): To determine the vapor pressure of liquefied petroleum gases refer to GS (2.1) and of gasoline-oxygenate blend refer to GS (2.3). 1.2 Vapor pressure is an important physical property of volatile liquids. This test method is used to determine the vapor pressure at 37.8oC of petroleum products and crude oils with initial boiling point above 0oC. 1.3 Vapor pressure is critically important for both automative and aviation gasolines, affecting starting, warm-up, and tendency to vapor lock with high operating temperatures or high altitudes. Maximum vapor pressure limits for gasoline are legally mandated in some areas as a measure of air polution control. 1.4 Vapor pressure of crude oils is of importance to the crude producer and the refiner for general handling and initial refinary treatments. 1.5 Vapor pressure is also used as an indirect measure of the evaporization rate of volatile petroleum products. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.