This paper presents an experimental and theoretical study in order to expand the study of the behavior of rectangular pile group on oil-contaminated sand slope. Pile group of 2*3 with center-to-center pile spacing equal 4Dp and thickness of the contaminated layer equal 5Dp was considered. Contaminated sand layers were prepared by mixing sand with oil content of 6% by weight of dried sand. A broad series of conditions, including uncontaminated cases, was tested by varying parameters such as the length of piles and the edge distance of the piles relative to the slope crest. From the experimental and theoretical studies, it was noticed that the ultimate lateral load (Hu) is decreased in case of contaminated sand compared with clean sand, the ultimate lateral load (Hu) enhances by increasing pile length and the ultimate lateral load (Hu) in case of parallel direction is increased proportionally by (4-17) % compared with series direction. Moreover, there is a close agreement between the laboratory tests and finite element analysis results. The maximum difference between the laboratory and finite element results was about 15 %.