Method and apparatus for determining phase transition temperature using laser attenuation

Disclosed are methods and apparatus for determining phase transition temperatures and, more particularly, for determining cloud, fluidity, freezing, and haze points of hydrocarbon fuels and hydrocarbon/oxygenate fuel blends. The attenuation of laser light as it passes through the sample, then through a laser line filter, and then into a photodetector is used to determine the transition temperature.