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Salawati Basin has 0.5 BBO and 0.1 TCFG oil and gas resources respectively. Hydrocarbon is generated from Tertiary and Pre-Tertiary source rock. Several source rock studies have been conducted, such as in Sirga Formation (Late Oligocene), Kais Formation (Middle Miocene), and Klasafet Formation (Late Miocene). Lack of knowledge in characteristics and thermal modelling study or source rock in Sirga Formation and Pre-Faumai, also curiosity to observe basin reverse polarity occurence is intriguing to be researched further. The purposes of this research are to know: a.) Sirga Formation and Pre-Faumai Formation source rock characteristics to generate hydrocarbon in Salawati Basin; b.) Maturity values based on %Ro, Tmax and 1D basin modelling. Research methodology was carried out using petroleum geochmistry analysis, including: TOC, Rock Eval Pyrolisis, kerogen typing, vitrinite reflectance (%Ro) from 9 cutting samples. Based on TOC parameter, organic-rich materials in both formations show good to very good quantity. On the other hand, PY parameter shows fair to good potency quality as source rock to generate hydrocarbon. Kerogen type composition dominated NFA which indicates oxidizing marine or lacustrine depositional environment. Crossplots between HI and Tmax shows kerogen mixture type II/III which indicates transition environment (fluvio-deltaic) depositional environment. Sirga Formation and Pre-Faumai (Oligocene) show low level maturity based on %Ro and Tmax. On the contrary, based on 1D basin modelling maturity of the source rock on Warir-1X well and WIR-1A (outside research area) show higher level maturity (early to mid-mature) since Middle Pliocene and progressed into late maturity stage on oil generation since Early Pleistocene. Depocenter, generally act as mature kitchen where hydrocarbon generated. Basin polarity reversal occurred since Pliocene and changed basin configuration i.e depocenter from on southern area becoming on northern area