A process for the production of paper which includes the steps of providing an aqueous suspension containing cellulosic fibers, and optional fillers; adding to the suspension: (a) at least one charged organic polymer; and (b) an aqueous sol containing silica-based particles; wherein the sol has: (i) an S-value within the range of from 10 to 45%; (ii) a viscosity within the range of from 5 to 40 cP; and (iii) a molar ratio of SiO.sub.2 to M.sub.2O, where M is alkali metal or ammonium, within the range of from 10:1 to 40:1; and (III) forming and draining the suspension on a wire. The invention is further directed to processes for making paper wherein the added sol has: (i) an S-value within the range of from 10 to 45%; (ii) a viscosity within the range of from 5 to 40 cP; and (iii) a silica content of at least 10% by weight, or wherein the added sol has: (i) an S-value within the range of from 10 to 45%; (ii) a viscosity within the range of from 7 to 25 cP; (iii) a silica content of at least 10% by weight; (iv) a molar ratio of SiO.sub.2 to M.sub.2O, where M is alkali metal or ammonium, within the range of from 10:1 to 40:1; and (v) a pH of at least 10.6. The invention is further directed to a process for making paper wherein the added sol is modified by an aluminum-containing compound, a boron-containing compound or a mixture thereof and has: (i) an S-value within the range of from 10 to 45%; (ii) a viscosity within the range of from 5 to 40 cP; (iii) a silica content of at least 10% by weight; and (iv) a molar ratio of SiO.sub.2 to M.sub.2O, where M being alkali metal or ammonium, within the range of from 10:1 to 40:1.