The use of dielectric-barrier discharges (DBDs) is a mature technology originally developed for industrial ozone production. In this article, it is demonstrated that DBDs are also an effective tool to convert the greenhouse gases CH4 and CO2 to synthesis gas (syngas, H-2/CO) at low temperature and ambient pressure. The synthesis gas produced in this system can have an arbitrary H2/CO ratio, mainly depending on the mixing ratio of CH4/CO2 in the feed gas. Specific electric energy, gas pressure, and temperature hardly influence syngas composition. The amount of syngas produced strongly depends on the electric energy input. CO2-rich mixtures prevent carbon and wax formation. At fixed specific input energies, the maximum amount of syngas with low H-2/CO molar ratio is produced from a mixture of CH4:CO2 = 20:80. In a mixture of CK4:CO2 = 80:20, as high as 52 mol of H-2 and 14 mol of CO have been obtained from 100 mol of feed gas at a specific input energy of 87 kW h/(N m(3)). CH4 conversion reaches 64%, and CO2 conversion is 54%. High temperatures lead to wax formation and carbon deposition in CH4-rich feeding mixtures. Low gas pressures favor syngas production.