Abstract: The present invention relates to the exploration for and exploitation of formation hydrocarbons. According to the invention, a sample of material, representative of the impregnation with hydrocarbons of the rocks passed through, is taken during a drilling operation, with which sample a value of an emission flux, representative of the concentration of the fluorescent elements in the sample, and a value of a fluorescence quotient, which reflects the nature of the hydrocarbons present in the sample, are determined by spectrofluorimetry. The invention finds its application in analytical laboratories and on the drilling sites of petroleum production fields.