A method for preparing an alkoxy-functional organohydrogensiloxane oligomer, where the method comprises: 1) reacting starting materials comprising: a polyorganohydrogensiloxane oligomer of unit formula: (HR 1 2 SiO 1/2) e (R 1 3 SiO 1/2) f (HR 1 SiO 2/2) g (R 1 2 SiO 2/2) h (R 1 SiO 3/2) i (HSiO 3/2) j (SiO 4/2) k where subscripts e, f, g, h, i, j, and k have values such that 5 ≥ e ≥ 0, 5 ≥ f ≥ 0, 10 ≥ g ≥ 0, 5 ≥ h ≥ 0, subscript i is 0 or 1, 5 ≥ j ≥ 0, subscript k is 0 or 1, with the proviso that a quantity (e + g + j) ≥ 2, and a quantity (e + f + g + h + i + j + k) ≤ 50; and each R 1 is independently a monovalent hydrocarbon group of 1 to 18 carbon or a monovalent halogenated hydrocarbon group of 1 to 18 carbon atoms; an aliphatically unsaturated alkoxysilane of formula: where each R 2 is independently an aliphatically unsaturated monovalent hydrocarbon group of 2 to 18 carbon atoms, each R 3 is independently a monovalent hydrocarbon group of 1 to 18 carbon atoms, subscript c is 0 or 1; and a cobalt complex which comprises a dicobalt hexacarbonyl diphenylphosphinoalkane, thereby preparing a reaction product comprising the alkoxy-functional organohydrogensiloxane oligomer; and optionally 2) isolating the alkoxy-functional organohydrogensiloxane oligomer prepared in step 1). 1) reacting starting materials comprising: a polyorganohydrogensiloxane oligomer of unit formula: (HR 1 2 SiO 1/2) e (R 1 3 SiO 1/2) f (HR 1 SiO 2/2) g (R 1 2 SiO 2/2) h (R 1 SiO 3/2) i (HSiO 3/2) j (SiO 4/2) k where subscripts e, f, g, h, i, j, and k have values such that 5 ≥ e ≥ 0, 5 ≥ f ≥ 0, 10 ≥ g ≥ 0, 5 ≥ h ≥ 0, subscript i is 0 or 1, 5 ≥ j ≥ 0, subscript k is 0 or 1, with the proviso that a quantity (e + g + j) ≥ 2, and a quantity (e + f + g + h + i + j + k) ≤ 50; and each R 1 is independently a monovalent hydrocarbon group of 1 to 18 carbon or a monovalent halogenated hydrocarbon group of 1 to 18 carbon atoms; an aliphatically unsaturated alkoxysilane of formula: where each R 2 is independently an aliphatically unsaturated monovalent hydrocarbon group of 2 to 18 carbon atoms, each R 3 is independently a monovalent hydrocarbon group of 1 to 18 carbon atoms, subscript c is 0 or 1; and a cobalt complex which comprises a dicobalt hexacarbonyl diphenylphosphinoalkane, thereby preparing a reaction product comprising the alkoxy-functional organohydrogensiloxane oligomer; and a polyorganohydrogensiloxane oligomer of unit formula: (HR 1 2 SiO 1/2) e (R 1 3 SiO 1/2) f (HR 1 SiO 2/2) g (R 1 2 SiO 2/2) h (R 1 SiO 3/2) i (HSiO 3/2) j (SiO 4/2) k where subscripts e, f, g, h, i, j, and k have values such that 5 ≥ e ≥ 0, 5 ≥ f ≥ 0, 10 ≥ g ≥ 0, 5 ≥ h ≥ 0, subscript i is 0 or 1, 5 ≥ j ≥ 0, subscript k is 0 or 1, with the proviso that a quantity (e + g + j) ≥ 2, and a quantity (e + f + g + h + i + j + k) ≤ 50; and each R 1 is independently a monovalent hydrocarbon group of 1 to 18 carbon or a monovalent halogenated hydrocarbon group of 1 to 18 carbon atoms; an aliphatically unsaturated alkoxysilane of formula: where each R 2 is independently an aliphatically unsaturated monovalent hydrocarbon group of 2 to 18 carbon atoms, each R 3 is independently a monovalent hydrocarbon group of 1 to 18 carbon atoms, subscript c is 0 or 1; and a cobalt complex which comprises a dicobalt hexacarbonyl diphenylphosphinoalkane, thereby preparing a reaction product comprising the alkoxy-functional organohydrogensiloxane oligomer; and