Late Oligocene coal-bearing horizons are found in the state of Arunachal Pradesh, Nagaland, and Assam and are associated with Tikak-Parbat Formation of Assam- Arakan Basin, northeast India. The Makum coalfield in Assam exhibits a considerable thickness of these late Oligocene coals. In the present study, organic geochemistry and petrography were applied on Makum coals for evaluating the source, thermal maturity, and hydrocarbon generation potential of organic matter. Petrography reveals that vitrinite constitutes the dominant maceral group (80.2–92.5% on a vmmf basis), followed by liptinites (4.0–15.4% vmmf) and inertinites (2.6–6.1% vmmf). High TOC (65.02–76.79%) and S2 (225.74–305.42 mg HC/g rock) values from Rock–Eval pyrolysis depict that the studied coal samples are prolific hydrocarbon source rocks. High hydrogen index (HI: 305–424 mg HC/g TOC) and low oxygen index (OI: 2–7 mg CO2/g TOC) classify the organic matter of the studied samples as hydrogen-rich Type II to II/III kerogen. Furthermore, petrographic study shows sufficient quantity of hydrogen-rich liptinite macerals. Rock–Eval Tmax (419–436 ºC) and vitrinite reflectance (0.49–0.52%) values with a very low production index (PI: 0.01–0.05) suggest that the coals are thermally immature. High HI and genetic potential (GP) values depict that these late Oligocene coals may produce mixed oil and gas upon maturation.