Abstract: Wells of subterranean siliceous formations containing hydrocarbons are stimulated by the injection of crosslinked acid polymers wherein the polymer is a polysaccharide selected from the group consisting of carboxymethyl hydroxypropyl guar and carboxymethyl hydroxyethyl cellulose. The crosslinked acid polymer is a gel formed from a hydrated polysaccharide sol containing from about 1 to about 15 weight percent hydrochloric acid and from about 0.2 to about 6 weight percent hydrofluoric acid to which a water hydrolyzable polyvalent metal salt is added to cause the crosslinking. The metal salt is zirconium, titanium or hafnium. Additionally, an adjunct salt can be added in an amount of from about 5 to about 50 pounds per 1,000 gallons acid prior to the addition of the hydrolyzable polyvalent metal salt.