An additive for drilling fluids employed in the deep well drilling industry, which additive comprises an organometal compound of titanium, zirconium or vanadium with humic acid and a further organic moiety which is at least one of fatty acid alkoxylates, fatty alcohol polyalkylene glycol ethers, long-chain amine alkoxylates optionally substituted with a hydroxyl group, or water-insoluble polyalkoxylate all of which are optionally mixed with fatty acids, and fatty acids alone, these having optionally been applied onto an inorganic carrier, mandatorily in the case of fatty acids alone. The fluid loss additive prevents the drilling fluid from streaming into porous drill formations. The additive may be prepared by the reaction of a metal alcoholate with a compound providing the organic moiety and humic acid or a humic acid-containing product.