This study examined the influence of hydrocarbon contamination arising from artisanal crude oil refining on the geotechnical properties of soils in Marine Base, Port Harcourt, Nigeria. The increasing prevalence of illegal refining activities in the Niger Delta has resulted in widespread soil pollution, raising concerns about the suitability of affected soils for engineering applications. Soil samples were collected from three contaminated locations (B1, B2, and B3) and one uncontaminated control site at a depth of 1 m. Laboratory analyses were conducted to determine key geotechnical parameters, including moisture content, Atterberg limits, particle size distribution, permeability, and compaction characteristics. The results showed that hydrocarbon contamination significantly altered the engineering behavior of the soils. Moisture content values in contaminated samples ranged between 16.5% and 22.4%, exceeding those of the control soil, indicating increased water retention due to oil presence. The Atterberg limits revealed increased plasticity, with plasticity indices ranging from 17% to 22%, suggesting higher compressibility and deformation potential. Particle size distribution analysis indicated aggregation of finer particles, resulting in modified soil gradation. Permeability values decreased considerably in contaminated soils, with hydraulic conductivity reducing to 3.8 × 10⁻⁴ cm/s compared to 6.5 × 10⁻³ cm/s in the control sample, reflecting restricted fluid flow due to hydrocarbon coating of soil particles. Compaction tests revealed a reduction in maximum dry density from 1.85 g/cm³ in the control soil to values between 1.62 g/cm³ and 1.72 g/cm³ in contaminated soils, alongside an increase in optimum moisture content from 14.5% to between 18.6% and 21.2%. These findings demonstrate that hydrocarbon contamination adversely affects soil strength, permeability, and compaction behavior, thereby reducing load-bearing capacity and increasing the risk of structural failure. The study highlights the need for effective remediation strategies and careful geotechnical evaluation before construction in contaminated areas. The results provide valuable insights for engineers, environmental scientists, and policymakers working in oil-impacted regions.