A drilling fluid comprising a pyruvate-free xanthan, which may be an
acetate-free pyruvate-free xanthan, and a high density calcium-based
brine. Preferably the pyruvate-free xanthan is a genetically prepared
pyruvate-free xanthan. A process for recovering crude oil from an
oil-bearing subterranean formation by drilling the formation and using a
drilling fluid comprising a pyruvate-free gum and a high density
calcium-based brine.