The determination of olefin contents in liquid hydrocarbons by means of laser-based infrared spectroscopy was demonstrated for the first time in this work. This new technique utilizes a commercial mid-infrared external-cavity quantum cascade laser and a photoacoustic detector to monitor characteristic olefin C=C absorption bands in the similar to 1640-1680 cm -1 (5.95-6.1 mu m) region. It is suitable for measurements of olefin concentrations in a variety of samples, including those derived from partially upgraded bitumen. To confirm this capability, olefin concentrations in the solutions of model compounds, thermally cracked and hydrotreated naphthas, and actual olefin-rich distillate samples were measured. This investigation showed that infrared lasers create a viable alternative to the conventional NMR and chemical methods widely used to determine the olefin contents in hydrocarbon feedstocks and products.