An ash fusion temperature reducing agent principally comprising at least 50.0 wt. % of a manganese compound, such as MnO, and the remainder of the agent comprising a silicon compound, such as SiO.sub.2 is mixed with an ash-containing fuel comprising a pumpable liquid hydrocarbonaceous material and/or petroleum coke to produce Mixture A. In one embodiment, the ash fusion temperature reducing agent comprises a comminuted pyrolusite ore in which the following elements are present in weight percent basis ore: manganese in the range of about 50-75, calcium in the range of about 0-1.0, silicon in the range of about 0-3.0, magnesium in the range of about 0-1.0, and aluminum in the range of about 0-1.0. Mixture A is reacted with a free-oxygen containing gas in a free-flow refractory lined reaction zone of a partial oxidation gas generator. A hot raw effluent gas stream comprising H.sub.2 +CO along with molten ash having a reduced initial deformation temperature are produced at a lower temperature. Alternatively, Mixture A may be first introduced into a coking zone and converted into petroleum coke in which the ash fusion temperature reducing agent is dispersed throughout. The petroleum coke entrained in a liquid or gaseous carrier is then introduced into the partial oxidation gas generator where a hot raw effluent gas stream comprising H.sub.2 +CO is produced along with molten ash having a reduced ash fusion temperature. The molten ash is readily separated from the effluent gas stream; and, the gas generator may be operated at a lower temperature thereby extending the life of the refractory lined reaction zone.