Abstract: Synthesis gas is produced by the partial oxidation of a feedstock comprising petroleum coke and/or heavy liquid hydrocarbonaceous fuel containing sulfur and having an ash that contains nickel, vanadium and a comparatively low level of silicon. An iron-containing additive is introduced into the reaction zone along with the feed. The additive combines with at least a portion of the nickel constituents and sulfur found in the feedstock to produce a liquid phase washing agent that collects and transports at least a portion of the vanadium-containing oxide laths and spinels and other ash components out of the reaction zone. In another embodiment, a minor amount of an additional material selected from the group of elements consisting of magnesium, chromium and mixtures thereof is included in the iron-containing additive. In still another embodiment, the iron-containing additive is uniformly dispersed in petroleum coke having a nickel and vanadium-containing ash.