Argilliferous limestone reservoirs usually are of high argillaceous content (3,~8,) but low logging resistiv-ity values in YL-DS Oil Field,Middle East.Interpreted as high water saturation by the conventional logging method,they are likely mistakably judged as aquifers according to the evaluation standard for the pure carbonate reservoirs.A simple available method of correctly identifying what the fluids are in argilliferous limestone reservoirs according to spectral log data and other calculations is put forward and successfully applied in this oil field.The method is:(1) ana-lyze clay types by spectral log data and estimate density of dry clay;(2) calculate porosity of pure mudstone by the simplified mudstone model,and then calculate the porosity related with argillaceous bound water in the argilliferous limestone reservoirs; (3) correct argillaceous bound water saturation with the water saturation calculated by normal Archieˊs formula to obtain water saturation in apparent pure limestone; and (4) comprehensively identify fluid types by the corrected pure limestone saturation and the standard cross-plot of pure limestone reservoirs.