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Although the Late Oligocene - Early Miocene Kujung Formation is one of the important exploration targets in the Kangean PSC Block where JAPEX share the interest with Mitsubishi Corporation and Energi Mega Persada, no commercial hydrocarbon accumulation from this formation have been discovered yet in the block. In the Kangean area, the relationship between facies and reservoir quality in the Kujung Formation carbonates are not well understood. In this study, geological survey in Kangean Island and petrological analysis using outcrop samples(totally 88 samples)were conducted to evaluate reservoir qualities of the Kujung Formation carbonates. Our study reveals that the Kujung Formation in the island is divided into 10 facies (F0 - F9) based on lithology, texture, sedimentary structures and bioclastic content. These facies are grouped into 3 facies associations (FA1-FA3) based on large scales depositional environments. Reservoir qualities of the Kujung Formation are generally controlled by pore system related with the facies associations and diagenesis. Since mechanical/chemical compaction during burial diagenesis is the most common effect on shelf slope and outer shelf facies, these sediments have micro porosities or are tight carbonates. These show permeability lower than 2 mD regardless of porosity values. In contrast, moldic/vuggy porosity is abundant in shallow marine facies by calcite cementation in interparticle porosity and dissolution of carbonate grains. These facies show fair to excellent reservoir qualities. Furthermore, results of core plugs and thin-sections analysis and observation indicate that connectivity of secondary pores is critical for enhanced permeability commonly by solution-enlargement. Our study also implies that shallow marine facies are likely to undergo multi-phase subaerial exposure events causing improvement of reservoir quality rather than outer shelf slope and outer shelf facies. [ABSTRACT FROM AUTHOR]