Abstract: Based on statistic and compared all available definitions of tight oil given by oil exploration scholars across the world, it can be defined that tight oil, which can be economically recovered only by large fracturing, is continuously accumulated within the source rock as well as its top and bottom, with tight clastic rock and carbonate rock as the reservoir rock, permeability less than 1 mD and porosity less than 12%. According to 8 parameters summarized after successful exploration and development of mature shale blocks in North America,the tight oil is of 10 accumulation characteristics: (a) special shale type is required; (b) organic matter abundance reaches a given level; (c) organic matter thermal maturity lies in the oil window; (d) organic matter type is mainly Type I and Type II; (e) organic?rich shale thickness reaches a given scale; (f) interbeds with good porosity and permeability exist between shale rocks; (g) overpressure conditions exist; (h) shale has high Young’s modulus and low Poisson’s ratio; (i) brittle minerals content is high; (j) crude oil is light. On these bases, this paper points out the differences between tight oil and shale gas in source rock quality and reservoir characteristics for economic development, and presents the assessment criteria for potential shale in tight oil basins from analyzing the geological conditions of tight oil accumulation in North America: TOC>2%, Ro: 0.5%~1.3%, ρr<0.87 g/cm3, μo<10 mPa·s. According to this criteria, 98 basins with tight oil exploration potential have been screened out across the world, their tight oils are mainly distributed in Mesozoic and Paleozoic