Massive consumption of petroleum since the past century has led to considerable emissions into marine ecosystems. Marine sediments may accumulate substantial quantities of petroleum and associated contaminants in oil-producing areas. Here, we report accelerated accumulation of total petroleum hydrocarbons (TPH) in 'blue carbon' vegetated ecosystems of the Arabian Gulf - the world's most important region for oil production. In addition to increased accumulation with the onset of oil exploitation, sediment records reflect a large depositional event associated with the 1991 Gulf War, with the magnitude of these maxima varying across habitats, depending on their elevation along the shoreline. Blue carbon ecosystems of the Arabian Gulf currently bury about 2300 megagrams (Mg) of TPHs annually and have accumulated TPH stocks of 59,799 Mg over the past 25 years alone. Massive burial and sequestration of TPH by blue carbon ecosystems is an important, but thus far unrecognized, removal mechanism in the Arabian Gulf. Conserving these ecosystems is important to avoid possible remobilization of sequestered TPH into the surrounding environment.