The present study focuses on the pyrolysis characteristics of OPF (oil palm fiber) and OPFP (oil palm fiber pellet) in N-2 and CO2 to evaluate the impacts of biomass pattern and carrier gas on the three-phase products. Three different reaction temperatures of 400, 450, and 500 degrees C along with 30 min pyrolysis are considered. The results indicate that OPFP pyrolysis gives a higher liquid yield when compared to OPF pyrolysis, and the liquid yield using CO2 as a carrier gas is higher than that using N-2. The influences of carrier gas and biomass pattern on the components in bio-oils are not profound. The deoxygenation and dehydrogenation mechanisms on solid biomass are obviously exhibited, and the latter is more pronounced than the former. The higher heating values of OPF and OPFP from pyrolysis are intensified up to 39 and 24%, respectively. The CO2 and CO concentration distributions suggest that the most drastic pyrolysis reaction develops at 7-9 min. On account of more energy required for breaking methoxyl groups, CH4 formation is later than CO and CO2 formations. In summary, OPFP pyrolyzed in a CO2 environment is a feasible operation for producing bio-oils, thereby saving facility space and CO2 utilization. (C) 2015 Elsevier Ltd. All rights reserved.