2020 Published with permission by the ICE under the CC-BY 4.0 license. This paper presents a detailed analysis of the effect of oil contamination on the geotechnical behaviour of bridge pile foundations, focusing on the influence of soil type, oil-contamination intensity and oil-contamination depth. A thorough parametric study of these dominant parameters was carried out through numerical analyses that were performed using Flac3D software. The analyses were designed using three types of soils: Poorly graded sand (SP), silty sand (SM) and kaolinite clay. Oil contamination degrades the geotechnical behaviour of bridge pile foundations. Soil type has a clear effect on the internal forces induced in the piles, with maximum normal forces occurring in SP, the maximum bending moment in kaolinite clay and maximum shear forces in SM. The variation of oil-contamination intensity in the soil changes the induced internal forces in the piles by ratios increasing to 40, 34 and 20% of the bending moment, the shear forces and the normal forces, respectively. However, the alterations in the displacements of the soil and the piles are more significant, with ratios up to 150%. In contrast, the oil-contamination depth has a limited effect on the internal force of the pile (up to 4%) but has a considerable effect on the displacement of the foundation.