Abstract: A method of stimulating production in sandstone formations of oil and gas wells is achieved by using an acid system which slowly dissolves the silicate and clay formations of the sandstone to increase its permeability. The acid system uses phosphonate compounds, including phosphonate acids and the salts and esters thereof, in combination with hydrofluoric acid. The hydrofluoric acid may be provided by hydrolyzing ammonium bifluoride or hydrofluoric acid itself. The phosphonate compounds of the acid systems retard the rate at which the hydrofluoric acid reacts with the clays while enhancing the reaction rate with silica, which comprises the bulk of sandstone formations. This allows more penetration of the formation immediately adjacent to the wellbore. The phosphonate materials also improve the dispersion and suspension properties of the treating solution with silts and fines and improves the complexing capacity of the acids with silicate and alumni complexes.