Raman spectrometers are employed in a hydrocarbon processing plant for online measurement of at least one compositional property of a hydrocarbon stream. The Raman spectrometers can be used to control separations equipment, determine energy content, and/or determine flow rate. The Raman spectrometers are especially advantageous when employed in a liquefied natural gas (LNG) plant to determine properties of cooled natural gas streams.
