The hydration of clays and shale in drilling operations may be inhibited by employing an aqueous based drilling fluid comprising a shale hydration inhibition agent having the formula wherein R is an alkyl group having 1 to 6 carbons, R1 is an alkyl group having 1 to 18 carbons, and X is an anion. The shale hydration inhibition agent should be present in the aqueous based drilling fluid in sufficient concentration to reduce the reactivity, such as swelling, of clays and shale when exposed to water-based drilling fluids.