In order to investigate quantitative grain fluorescence responding to residual oil zones and palaeo-oil zones, samples from sandstone reservoirs in well TZ421 in Tazhong area, Tarim Basin, NW China, were used to carry out quantitative grain fluorescence (QGF and QGF-E) measurement and analysis. A palaeo-oil zone can be delineated in well TZ421 between 3 720 and 3 620 m with strong QGF responds. A residual oil zone was discovered in well TZ421 between 3 680 and 3 620 m with strong QGF-E responds. The presence of a residual oil zone and a palaeo-oil zone in well TZ421 below the current oil-water contact indicates that some oils were lost after the initial charge. The reservoir is believed to have been charged initially down to 3 720 m at the depth of the palaeo-oil-water contact. The presence of a 60 m residual oil zone below the current oil-water contact, as delineated by QGF-E, suggests that the palaeo-oil zones leaked in two epochs and part of the oil lost quite recently. The strong QGF responds in the current condensate gas interval indicates that the initially charged oil was partly displaced by gas and formed an oil zone with a gas cap.