The technology relates to a method of producing synthesis gas comprising carbon monoxide (CO) and hydrogen (H2), wherein the synthesis gas is produced by a reduction reaction of a first flow comprising a carbon source and an excess of hydrogen in contact with an Oxy-flame. The hydrogen comes from a reducing stream, a first portion of which ends up in the first flow, and a second part of which is used to generate the Oxy-flame by combustion of the hydrogen in the presence of a second flow comprising oxygen (O2), the second flow coming from an oxidizing stream. The first flow and the second flow are at a distance from each other such that the Oxy-flame supports the reaction between the carbon source and the hydrogen. A reactor, which can have different configurations, is also proposed for implementing the method.