A method of drilling a well bore into a subterranean formation containing water with monovalent and polyvalent cations and preventing leak-off into the formation of an oil-base drilling fluid used in the drilling. The method is carried out by adding to an oil-base fluid comprising an oil, water, a weighting agent and an emulsifying agent, a powdered seepage loss reducer selected from the group consisting of an amorphous silicate having a molecular ratio of silicon dioxide to alkali metal oxide in the range of from about 1.5:1 to about 3.3:1 wherein the alkali metal is selected from the group consisting of sodium, potassium, and mixtures thereof, an ammonium soap of a fatty acid having from about 12 to about 22 carbon atoms and mixtures thereof to form the drilling fluid and circulating the drilling fluid containing the powdered seepage loss reducer in the well bore. When the circulation of the drilling fluid containing the seepage loss reducer takes place, the compound reacts with the monovalent and polyvalent cations contained in the formation to form a seal in the formation adjacent to the well bore.