This research investigated the bearing capacity and geotechnical properties of a sandy soil substrate contaminated with the oil derivatives diesel fuel and kerosene. For this purpose, a site with a clayey sandy soil substrate was considered to evaluate the effects of contamination on the geotechnical properties and bearing capacity of the substrate in both clean and contaminated states. Then, the substrate of the site was artificially contaminated with diesel fuel and kerosene and underwent field and laboratory tests. The experiments, including the Atterberg limits, standard Proctor compaction, uniaxial compressive strength, strength and freeze–thaw durability tests, were performed on prepared samples. Also, to determine the bearing capacity of the contaminated and intact substrates, a plate load test was conducted at the site. The results indicate that contamination by oil derivatives reduces the strength and increases the settlement and displacement of the contaminated substrate, where the effects of diesel fuel are more significant than those of kerosene. The results of this research are compared with those of previous studies. The literature shows that most research in this area was carried out in the laboratory, and there is a lack of in situ studies. This study showed that the presence of oil contaminations caused a 3.5% reduction in the soil Atterberg limits. The contaminations also reduced the dry density and uniaxial compressive strength of the soil by 2.5% and 20%, respectively. The results presented were consistent with those of other researchers. However, some studies have suggested an increase in the Atterberg limits owing to oil contaminants in the soil.