||Steam reforming, CO2 reforming, and simultaneous steam and CO2 reforming of methane to CO and H2 over NiO-CaO catalyst (without any prereduction treatment) at different temperatures (700-850 ° C) and space velocities (5000-70\,000 cm3$\cdot$g-1$\cdot$h-1) are investigated. The catalyst is characterized by XRD, XPS, and temperature-programmed reduction (TPR). The catalyst showed high activity/selectivity in both the steam and CO2 reforming reactions and the simultaneous steam and CO2 reforming. In the CO2 reforming, the coke deposition on the catalyst is found to be very fast. However, when the CO2 reforming is carried out simultaneously with the steam reforming, the coke deposition on the catalyst is drastically reduced. By the simultaneous CO2 and steam reforming (at $\geq$800 ° C and space velocity of about 20\,000-30\,000 cm3$\cdot$g-1$\cdot$h-1), methane can be converted almost completely to syngas with 100% selectivity for both CO and H2. The H2/CO ratio in products can be varied between 1.5 and 2.5 quite conveniently by manipulating the relative concentration of steam and CO2 in the feed.