A water based drilling fluid contains as additive one or more alkyl ethoxylates having the formula RO(CH.sub.2CH.sub.2O).sub.nH; wherein: R is a C.sub.16-22alkyl group (preferably R is aliphatic and more preferably R is linear), and n is an integer in the range 2-30. The fluid further contains one or more viscosifying agents, and is substantially clay-free.