The present invention relates to a method of detecting a counterfeit, or adulterated petroleum fuel, comprising: a) emitting a modulated light beam from a modulated light source to a marked petroleum fuel in a chamber, wherein the marked petroleum fuel comprising a fuel additive, a mixture of a fluid petroleum fuel and a marker, wherein the marker is selected from the group consisting of organic IR absorbing compounds and mixtures thereof; b) producing an acoustic signal from the marker in the chamber, in response to the emitted modulated light beam; c) detecting the acoustic signal via a sensor disposed in the chamber; d) transmitting the acoustic signal from the sensor to a processor based module; and determining the marker and a concentration of the marker in the marked petroleum fuel via the processor based module, from the acoustic signal.