A silver impregnation solution comprising: (i) silver ions, (ii) a silver concentration enhancer selected from at least one ammonium salt having an anionic component that is thermally decomposable; or at least one amino acid, or a combination thereof, (iii) at least one organic amine; and (iv) water; wherein said components (i)-(iii) are dissolved in said impregnation solution, and oxalic acid may or may not be included. The silver impregnation solution can achieve significantly higher silver concentrations, including at least or above 33, 34, or 35 wt %. Methods for producing a silver catalyst by silver impregnation of a refractory support followed by calcination are also described. The resulting silver catalysts possess high silver loadings of typically at least 17, 18, or 19 wt %.