Conversion of syngas to high octane olefinic naphtha

In a syngas conversion process wherein a mixture of gaseous carbon oxides and hydrogen at hydrogen donors is contacted at elevated temperatures and pressures with a Fischer-Tropsch catalyst, the improvement which comprises carrying out said conversion at a temperature of from 500.degree. to 800.degree. F., a space velocity of from 1000 to 30,000 GHSV, and a pressure of from 100 to 1000 psig with a catalyst composite comprised of an intimate mixture of an iron Fischer-Tropsch component and a component containing an acidic solid wherein the volume ratio of said component containing an acidic solid to said iron Fischer-Tropsch component is 1-20, said acidic solid being selected from the group consisting of hydrogen exchanged silica-alumina, silica-magnesia, erionite, mordenite, faujasite, and ZSM-4 with the proviso that when the acidic solid is silica-alumina or silica-magnesia, the temperature is at least 600.degree. F., and with the further proviso that when the acidic solid is a zeolite, the zeolite has no more than 0.5 wt.% of alkali metal cations associated therewith, and recovering a product comprising an olefinic naphtha having a boiling range of less than 400.degree. F. at 90% overhead with an aromatic content less than 20 weight percent, an olefin plus aromatic content of at least 50 weight wherein the olefins have predominantly internal double bonds.