A petrographic study was carried out on boreholes Kudu 9A-2 and 9A-3. The gas-bearing reservoir target interval can be divided into a lower non-marine unit and an upper marine unit. The non-marine unit generally has very good reservoir characteristics with good secondary porosity after the leaching of calcite cement. The present porosity and permeability of these sandstones are determined by the distribution of silica cement, which in turn was controlled by the original carbonate and evaporite cementation of the sandstones. The marine unit comprises a shelly sandstone and a lithic sandstone facies, and has poor reservoir characteristics. Low initial permeabilities in the marine sandstones resulted in the limited passage of pore fluids, an almost closed system and therefore limited authigenesis. The shelly sandstones were pervasively cemented by calcite during shallow burial. Their interbedded nature and fine grain size inhibited dissolution of the calcite, effectively halting diagenesis at that time. The lithic sandstones underwent limited diagenesis and compaction of the ductile lithics resulted in the formation of abundant pseudomatrix. During burial, the alteration and breakdown of igneous clasts resulted in chlorite authigenesis, whereas quartz overgrowths developed where initial porosity was slightly better.