The catalytic properties of dense fluorite-structured Bi1.5Y0.3Sm0.2O3-delta (BYS) pellets for oxidative coupling of methane (OCM) to ethane and ethylene (C-2 products) were studied in a packed-bed reactor in co-feed mode. The effects of temperature, feed flow rate, CH4/O-2 and He/(CH4 + O-2) ratios on the OCM performance over BYS were systematically investigated. The appropriate operating conditions were found to be: temperature, 900-1000 degreesC; total flow rate, 90-150 ml (STP)/g min; CH4/O-2 ratio, 2-3.5; He/(CH4 + O-2) ratio, 0.75-1.75. Under these conditions, C-2 yields of 20-27%, C-2 selectivities of 50-62% and C2 space-time yield of up to 6.9 mu mol/g s were achieved. The good OCM catalytic properties of BYS are believed to be related to its fluorite-type phase structure and large oxygen ion mobility at high temperatures. OCM kinetics of BYS oxide was studied with the assumption that no C2 products were converted to CO, under low to medium methane conversion range. Lumped rate equations for C-2 and COx formation were obtained as functions of temperature, O-2 and CH4 partial pressures. The solid phase oxygen ions are responsible for the C-2 formation, while the gas phase oxygen molecules enhance the COx formation.