Primary stragraphic traps in sandstone in-valve lateral termination of the reservoir as a direct or indirect result of factors related to the depositional environment. Red Wash, Coalinga East, Pembina, Mistsue, Bell Creek, Cut Bank, Burbank, and Bradford are among the very few giant oil accumulations found in such traps. As these traps rarely can be detected by surface measurements, other discovery methods are essential. The understanding f depositional process and environment is a promising approach.