Aliphatic hydrocarbon residues were monitored in two fish species, Indian mackerel (Rastrelliger Kanaguria) and Indian scad (Decapterus russelli) collected from local markets in three different cities in Oman. Residues were also monitored in water samples collected from two sites of the Gulf of Oman. Sampling was conducted twice, in July and again in February to have a thorough understanding of the dynamics of aliphatic hydrocarbon residues. Results indicated the presence of petrogenic aliphatic hydrocarbons ranging from C12-C28 in fish and water samples alike. Fish and water chromatograms were characterized by an unresolved complex mixture (UCM), a confirmatory sign of petrogenic origin of monitored hydrocarbons. Residue levels showed some variations related to sampling sites and time of sampling.