Abstract: The south terrace in Gaoyou sag is presented, according to the analysis of the structural evolution section. That is, when the Sanduo movement ended, the south terrance activity tended towards calming down, and all faults in it stopped acting, accordingly, hence forming present structural framework. Once shaping a good match between the fault-active period and hydrocarbon-migrating period, could the faults become major channels for vertical migration of hydrocarbons and lateral crosscutting followed by forming favorable hydrocarbon traps in Gaoyou sag.

Key words: Gaoyou sag, south terrace, structural evolution, developed sequence, hydrocarbon accumulation, control