Abstract: The Mesopotamia Basin is one of the most prolific petroliferous basins in the world.The most important productive layer is Cretaceous.Based on the comprehensive analyses of structure,sedimentary,drilling and testing,the paper summarizes the controlling factors of hydrocarbon accumulation.They are high-quality source rocks,good reservoir-seal assemblages,huge structural traps,migration pathways and so on.There are two kinds of accumulation models in the Mesopotamia Basin.In the center and south of the basin,petroleum gene-rates in the lower formation and is reserved in the upper formation.Carrier beds are the main pathways for oil-and-gas migrations in the parallel direction.The characteristics of petroleum are controlled by source rocks.In the north,oil and gas migrate from the Jurassic and the Lower Cretaceous source rocks to the Upper Cretaceous reservoirs along strike slip faults.The differential hydrocarbon accumulations lead to light oil in the lower formation and heavy oil in the upper formation.