NOVELTY - Forming a hydrocarbon fuel involves forming syngas from fossil-fuel hydrocarbon feed; adding the stream to a carbonaceous feed based syngas stream; converting the mixed syngas stream to form product fuel and recovering a byproduct stream comprising at least one of hydrogen, carbon monoxide, water vapor, methane, and at least 2C(preferably 2-8C) hydrocarbons containing 0 to 2 oxygen atoms; and reacting up to 100% of the byproduct stream with syngas stream.    USE - For producing a fuel from carbonaceous feed derived from gasification, using a fossil-fuel based hydrocarbon feed e.g. liquefied petroleum gas (claimed). The fuel includes e.g. ethanol, methanol, diesel.    ADVANTAGE - The process increases conversion of carbon monoxide generated in the biomass treatment step (e.g. gasification step) to product fuel which increases the output of the desired product fuel, e.g. ethanol, methanol, diesel, by virtue of the increase in the hydrogen:carbon monoxide ratio in the syngas fed to the catalytic/Fischer-Tropsch reactor; and is adjusted, in that the processing conditions can be adjusted in response to changes in the characteristics of the biomass, or changes in the desired product fuel (i.e. changes in the relative proportions of the different components of the fuel produced). The impact of the addition of the hydrogen-rich syngas stream on the overall carbon footprint of the facility that transforms biomass into fuel, as quantified in terms of CO2 emissions avoided. The fuel such as ethanol produced from this facility reduces anthropogenic CO2 emissions by replacing an equivalent amount of gasoline used as fuel in automobiles. Thus, increasing the fuel (ethanol) output of the facility through addition of the relatively hydrogen-rich stream has a positive impact, i.e. net CO2 emissions avoided increases, even taking into account the likelihood that the hydrogen-rich stream is typically produced from a fossil fuel, e.g. natural gas, in a way that results in additional CO2 emissions. The method enables reliance on selecting the process conditions for the syngas production reactor to maintain or preferably increase the net CO2 emissions avoided as compared to the base gasified biomass-to-fuel process without addition of the hydrogen-rich syngas stream. Fewer unit operations are needed for generation of the hydrogen-rich stream versus more than 99% H2. The system for generating the hydrogen-rich stream allows an easier way to optimize catalyst selectivity to drive the liquid fuel-forming reactions instead of reliance on the water-gas shift. In process achieves these advantages at low capital cost owing to needing fewer and less complex unit operations as compared to other possible approaches. Operating costs are reduced because of the increased fuel (e.g. ethanol) production from what is otherwise the same system.    DETAILED DESCRIPTION - Forming a hydrocarbon fuel involves forming a gaseous product stream comprising hydrogen and carbon monoxide at a mole ratio of H2:CO of at least 2:1, from fossil-fuel hydrocarbon feed; adding the product stream to syngas stream containing hydrogen and CO that is derived from carbonaceous feed material, in an amount to form a mixed syngas stream having H2:CO mole ratio greater than that of the syngas stream derived from carbonaceous feed material; converting the mixed syngas stream to form product fuel and recovering from it a byproduct stream comprising at least one of hydrogen, CO, water vapor, methane, and at least 2C (preferably 2-8C) hydrocarbons containing 0 to 2 oxygen atoms; and reacting up to 100% of the byproduct stream with gaseous product stream. An INDEPENDENT CLAIM is included for improving carbon conversion efficiency of fuel production from carbonaceous feed material, involving deriving a raw gaseous stream comprising hydrogen and carbon monoxide in a mole ratio of hydrogen:carbon monoxide of less than 2:1 from carbonaceous feed material; forming a second gaseous stream comprising hydrogen and carbon monoxide in a mole ratio of hydrogen:carbon monoxide greater than 2:1 and also comprising carbon dioxide, and combining the second gaseous stream and the stream derived in the deriving step; converting the combined stream into liquid product fuel, and a gaseous byproduct mixture comprising hydrogen, carbon monoxide, water vapor and methane; and reacting hydrocarbon fuel and steam to form the second gaseous stream, where at least a portion of the gaseous byproduct mixture is combusted to produce heat which is consumed in the reaction.