An aqueous slurry of a solid fuel and a process and a means for producing said slurry are described. The aqueous slurry comprises a highly concentrated slurry of a pulverized, carbonaceous material having a particle size of at most 0.5 mm, and 0.02-2% by weight of at least two surface active additives. The solids content of the slurry is 65-90% by weight, preferably 70-80% by weight. The slurry is characterized in that the surface active additives include, as a major part, a water-soluble nonionic surface active agent which is an alkylene oxide adduct with a hydrophobic part and a hydrophilic part, said hydrophilic part consisting of at least one polyalkylene oxide chain with a length of at least 40, preferably 50-150 ethylene oxide units; and, as a minor part, an ionic surface active agent.The ionic surface active agent preferably has the general formula: ##STR1## wherein R.sub.1 and R.sub.2 are hydrogen or an alkyl group with 1-22 carbon atoms, provided that the sum of the number of carbon atoms of R.sub.1 and R.sub.2 is at least 6, and Z.sub.1 designates the group --SO.sub.3 H, --CH.sub.2.sup.+ NHR.sub.3 R.sub.4 X.sup.- or --CH.sub.2.sup.+ NR.sub.3 R.sub.4 R.sub.5 X.sup.-, wherein R.sub.3, R.sub.4 and R.sub.5 are alkyl and/or hydroxyalkyl groups with 1-4 carbon atoms and X is an anion, and n is 40-200.