A short-term oil spill near the Turag River, Dhaka (Bangladesh), was investigated to characterize early stage hydrocarbon weathering at the molecular level. Spilled oil, oil-impacted sediment, and contaminated water samples were collected over a 19-day period at three sampling intervals and analyzed using negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry ((–) ESI FT-ICR MS) combined with ultrahigh-resolution liquid chromatography–mass spectrometry (LC/UHRMS). Across all matrices, acidic oxygen-containing (Ox) compounds increased during the early stages of weathering. Enrichment of water-soluble aromatic compounds, particularly O₃–O₅ classes at lower DBE values, is compatible with enhanced oxidation and dissolution of oil-derived components in the aqueous phase relative to sediment and bulk oil. Sulfur–oxygen (SOx) compounds also exhibited compositional changes consistent with oxidative transformation, reflected by an increase in SO₅ species in water accompanied by a corresponding decrease in SO₄ species in oil and sediment. Principal component analysis (PCA) differentiated oil-derived Ox compounds among the three environmental matrices along gradients of oxidation and solubilization. The observed molecular patterns suggest two dominant early-stage transformation pathways: transfer from oil to sediment followed by migration to water, and direct transfer from oil to water. Evaporation, dissolution, oxidation, and biodegradation are inferred to be the primary processes contributing to these initial compositional changes. Overall, this study provides molecular-level insight into short-term oil spill weathering under tropical freshwater conditions and identifies diagnostic molecular features useful for distinguishing petrogenic inputs from biogenic organic matter in complex aquatic environments.