The Late Eocene (?)/Oligocene-Recent Nakhon Basin located in the western portion of the Gulf of Thailand has a NWSE trending half-graben structure controlled by a NE dipping boundary fault on the SW margin of the basin. Six marker horizons were interpreted to determine significant geological events in the basin. Faults are subdivided into two sets based on orientation. The NW-SE, NE dipping boundary fault comprises two segments, Y and X. The two fault segments are inferred to follow NWSE pre-existing fabrics in the pre-rift section. The N-S trending fault sets are separated into two groups, early syn-rift faults and syn-rift faults. During the syn-rift stage (Oligocene-Middle Miocene), the basin was dominated by N-S early syn-rift faults then segment Y exhibited strong displacement in the Oligocene. The fault grew from several isolated strands, reached a maximum length then towards the end of extension. The western part of the fault remained active while the eastern part was inactive.
