A microprocessor-based XRF system utilizing a Si (Li) detector has been developed to perform quantitative concentration analysis in minutes with push-button operational simplicity.The instrument incorporates an air-cooled x-ray tube, providing either direct or filtered radiation. The excitation conditions are automatically set by software during instrument operation.Quantitation is performed using a modified Rasberry-Heinrich approach which recognizes x-ray intensities due to the elements in the sample, and calculates the influence of interelement effects on those intensities. The result, which is output to a 9″ video monitor, and 2¼″ thermal tape printer is in terms of familiar units of concentration: either weight percent or PPM. The data required for analysis (such as matrix correction or overlap factors) are stored in PROM; data reduction takes place in a 8-bit microprocessor, addressing 16K of RAM.Computer-controlled gain and offset adjustments provide automatic energy calibration. Day-to-day or long term intensity drifts are corrected automatically by use of an “intensity monitor” supplied with the instrument.The instrument is currently in general use primarily for the determination of concentration of S, Cl, Ba, Ca, Zn and P in new blended lubrication oils.