A method for supplying synthesis gas comprising reacting a carbonaceous feed with an oxidant, to generate synthesis gas; forwarding all or part of the generated synthesis gas to an underground storage location, to generate a synthesis gas buffer; and retrieving synthesis gas from the underground storage location and supplying the retrieved synthesis gas to a downstream processing unit, which downstream processing unit is substantially continuously converting synthesis gas. Conveniently the downstream processing unit can comprise a water-gas shift unit and the invention further provides a system for supplying synthesis gas comprising: a gasification unit, for generating synthesis gas from a carbonaceous feed and an oxidant, that is at least directly or indirectly connected to an underground storage location; an underground storage location, for generating a synthesis gas buffer, that is at least connected directly or indirectly to the gasification unit and at least connected directly or indirectly to a water-gas shift unit; and a water-gas shift unit, for generating a shifted synthesis gas, that is at least connected directly or indirectly to the underground storage location.