Abstract: A small portion of crude oil sample is introduced into the clean, dry and temperature-controlled oscillating U-tube, the change in oscillating frequency caused by the change in the mass of the U-tube is used in conjunction with U-tube constants previously determined by measuring the oscillation frequencies when the U-tube is filled with calibration fluids of known density to determine the density of the sample. This article present the method & principle for determination of density of crude oils by digital density analyzer and points for attention.