The influence of absorption effects in measuring elements in petroleum oil by X-ray fluorescence can, under certain circumstances, be predicted approximately from theory. Exact information on specific systems and instrumental conditions must practically be provided by experiment, however. The influence of absorption on fluorescent intensity under specific conditions of interest has been studied from three viewpoints; varying the depth through oil of a solid elemental specimen, varying the depth of a solution containing the element dissolved in oil, and varying the amount of the dissolved element in oil over a broad range in concentration. The group of elements selected for study illustrate characteristic fluorescent radiations often1 measured from oil. The experimental results are expressed graphically and are compared between elements as well as with theory. The results have analytical implications which pertain to the quantitative determination of elements in oil by X-ray fluorescence.