Borehole data shows that alluvial fans and braided channels are dominant during early stage of deposition of the Phrae Basin Formation, while in the middle units lacustrine, peat swamp and poorly drained floodplain deposits alternate with braided channels and alluvial plains. Coal facies are commonly associated with lake margin and peat swamp environments in the middle units, although the western area contains thicker lacustrine and peat swamp sequences while alluvial plains and braided channels are dominant in the eastern part of the basin. In the Rong Kwang sub-basin no core is available but 2D seismic characteristics show that this part of basin was probably dominated by high energy fluvial deposits.