Hydrothermal carbonization (HTC) and its parameters show a significant role in the quality of HTC products and the distribution of yield. The present study investigates the optimal conditions that are suitable to produce maximum yield products of solid, liquid, and gas, from HTC of oil palm trunk (OPT), by following the Taguchi method. Moreover, all the three products of HTC were analyzed using various characterizations. The optimum runs for hydrochar yield, liquid yield, and gaseous yield were run 1 (R1), run 4 (R4), and run 9 (R9), respectively. The reaction temperature was found to be the most influential parameter that affected the yield distribution during HTC, where low temperature supported solid production, intermediate temperatures favored liquid yield, and high temperature produced higher gaseous yield. Elemental analysis, H/C and O/C atomic ratios, higher heating value (HHV), and energy density values of hydrochar recommended that the HTC process has significantly converted OPT into better energy fuel. The energy densification value of hydrochar ranged between 1.28 and 1.40, which confirmed the significance of the HTC process. Two characteristic peaks from FTIR were observed at 3,430 cm?1 and 2,923 cm?1 hydrochar. SEM analysis confirmed that the porosity of hydrochar was higher than OPT after HTC. However, the major organic matter in the bio-oil traced by GC-MS analysis was acetic acid, accounting for about 59.9-71.7%, and the outlet gaseous product consisted of 0.87-9.17% CH4, 3.88-29.02% CO2, 1.07-7.89% CO, and 0.31-1.97% H2, respectively, as shown by GC-TCD.