Abstract: The deposits of mouth bar and lakeshore bar are found at the middle oil-bearing assemblage (Qingshankou and Yaojia formations) in southern and western depositional systems, Songliao basin, characterized by large thickness and wide extension. The thick reservoirs with bottom water shaped by these bars are kinds of significant lithologic reservoirs in this area with high ratio of sand/total strata thickness. Based on the 0-rigin, distribution and internal structure of the bars, the genetic relationship between the bars and faults of minor slip and structures of low am-plitude is discussed. The petroliferous features of the bars are analyzed,by which the petroleum accumulation mechanism,mainly controlled factors and distribution are revealed, and the favorable target areas for petroleum exploration are pointed out in this paper.

Key words: Songliao basin, mouth bar, lakeshore bar, thick strata, bottom water reservoir, petroleum accumulation