We report a pulsed‐dye‐laser optoacoustic spectroscopy technique for sensitive measurements of weak absorption spectra of liquids. We have used this technique to measure the weak visible absorption band of benzene near 607 nm, due to the sixth harmonic of the C‐H stretch. We obtain a signal‐to‐noise ratio exceeding 102at the absorption peak. We estimate that with improved data handling, absorption features as small as 10−7cm−1should be detectable in liquids. This opens up new possibilities of trace‐constituent detection and pollution monitoring in the liquid phase.