The disclosure relates to a system and method for analyzing a gaseous sample extracted from a drilling fluid coming from a wellbore. The system comprises a surface assembly, situated outside of the wellbore and including: an extractor for extracting a gaseous sample from the drilling fluid, a quantification device connected to the extractor for quantifying at least a gaseous constituent contained the gaseous sample. The quantification device comprises at least a photoacoustic cell in fluid communication with the extractor, at least a light source for emitting a light beam at a predetermined emission spectrum in the photoacoustic cell, at least an acoustic detector positioned in the photoacoustic cell and a processor for calculating a parameter relative to the quantity of the gaseous constituent on the basis of a signal obtained from the detector.