Empty fruit bunch (EFB) and bagasse, which are now and in near future quite abundant biomass residues in Southeast Asia, were gasified using steam or (steam + oxygen) as a gasification agent in an entrained-flow type gasification reactor at 900 °C. When using steam alone, EFB was gasified well (carbon conversion rate into gas was defined as "gasification rate": over 95%) and the hydrogen-rich gas suitable for liquid fuel synthesis ([H2]/[CO]=about 3-3.6) were obtained. Theoretical value of [H2]/[CO] required for many types of liquid fuel synthesis processes is about 2. However, hydrogen rich gas is desirable, because the processes are stabilized by the excess hydrogen. Bagasse was not so well gasified (gasification rate: about 90%) and the [H2]/[CO] was about 1.5-1.8, which was lower than that of EFB, in spite of being gasified under similar gasification conditions. When adding oxygen to steam, gasification rates of both EFB and bagasse were improved (over 98%). By adding oxygen, the [H2]/[CO] obtained from the EFB decreased from 3.6 to 2.7, which were still high enough for liquid fuel synthesis. The ratio from the bagasse decreased to 1.3, which was much lower than optimum value, 2, for liquid fuel synthesis. Tar yields of all the cases were quite low (<0.1 wt%), which were mainly composed of six poly-cyclic aromatic compounds, such as naphthalene. Solid residues yields of all the cases were also low. Solid residues obtained from the EFB were softened products, which partially adhered to the reactor. We also performed thermo-gravimetric (TG) analyses using a thermo-balance specially designed for analyzing feedstock in the presence of oxygen, steam, or both. The TG analyses showed that the EFB decomposed well in the presence of steam, oxygen or both, and that the bagasse did not well decompose in steam but well decomposed in oxygen or oxygen and steam. The TG analyses and the results of gasification were compared to each other and found to agree approximately. The EFB was gasified well using steam alone to produce hydrogen-rich gas suitable for liquid fuel synthesis, but treatment of solid residues would be required. The bagasse was also well gasified by adding oxygen to steam, but further adjustment of gas composition ([H2]/[CO]) would be required for liquid fuel synthesis.