A liquid gas vaporization and measurement system, and associated method, for efficiently vaporizing a continuous sample of liquid gas, such as liquid natural gas (LNG), and accurately determining the constituent components of the gas. A constant flow of liquid gas sampled from a mass storage device is maintained in a vaporizing device. Within the vaporizing device the liquid gas is flash vaporized within heated narrow tubing. The liquid gas is converted to vapor very quickly as it enters one or more independently operating vaporizer stages within the vaporizing device. The vapor gas is provided to a measuring instrument such as a chromatograph and the individual constituent components and the BTU value of the gas are determined to an accuracy of within +/−0.5 mole percent and 1 BTU, respectively.