Publisher Summary This chapter discusses the formation of ethane and ethylene by the reaction of methane and carbon dioxide over unsupported metal oxides and focuses on the effectiveness of metal oxide on C2 formation from CH4 and CO2 and elucidation of the catalytic performance of lanthanide (Ln) oxides with high C2 selectivity. In an experiment presented in the chapter, the reaction of CH4 and CO2 was carried out with a quartz-made fixed-bed reactor under atmospheric pressure. Thirty oxides including alkaline earth, rare earth, and transition metal oxides were used in these reactions. The reaction of CH4 and CO2 proceeded over all the oxides examined, except for CuO, which reacts only with CH4. The conversion ratios of CH4 to CO2 with most oxides were approximately 1:2, which means that CH4 and CO2 reacted overall with a molar ratio of 1:2. Most of lanthanide oxides show higher selectivity of C2H6 and C2H4 when the reaction of CH4 and CO2 is carried out at 850°C using the thirty oxides. Praseodymium (Pr) and terbium (Tb) catalysts are more effective for C2 formation among lanthanide oxides. The lattice oxygen atoms in Pr and Tb oxides are very mobile and, thus play a crucial role in C2 formation.