Chronic crude oil pollution remains a major environmental and engineering challenge in the Niger Delta. This study examines the short-term behavior of total petroleum hydrocarbon (TPH) fractions in a controlled water–soil system containing earthworms, with emphasis on the partitioning of hydrocarbons, changes in physicochemical parameters, and biological response. Crude oil (25 mL) was introduced into mesocosms containing 100 mL of water and 100 g of soil with acclimated earthworms for 48 hours. TPH fractionation in water, soil, and worm tissues was quantified using GC-FID (EPA 8015), targeting aliphatics (C5–C35), BTEX (benzene, toluene, ethylbenzene, xylenes), PAHs, and resin–asphaltene fractions. Results show minimal pH variation (6.82 – 6.85) and stable temperature (25.1 - 25.8 °C), indicating that mortality was chemically driven rather than physicochemical stress. Hydrocarbons partitioned predominantly to soil (712 mg/kg) and worm tissues (569 mg/kg), with water retaining only 1.55 mg/kg. Aliphatic fractions dominated accumulation in both soil and biota, while PAHs (including benzo[a]pyrene and pyrene) constituted key toxic components. All earthworms died within 48 hours, confirming acute toxicity. The engineering interpretation suggests reduced permeability, altered porosity, and potential weakening of soil structure due to hydrocarbon sorption. Findings demonstrate that TPH fractions significantly degrade ecosystem function and compromise the suitability of oil-impacted sediments for geotechnical applications. These results support improved remediation frameworks, contaminant monitoring, and engineering design considerations in petroleum-impacted regions.