A surfactant composition is used to repel down-hole fluids such as crude oil and water to prevent their adherence to a down-hole instrument for an extended period of time. A down-hole fluid repelling surfactant, preferably in the form of a liquid solution, is applied to an exterior surface of the instrument, dried, and polished to prevent down-hole fluids from adhering to the surface. A preferred liquid surfactant solution contains as an active ingredient an amount of tricresyl phosphate effective to repel down-hole fluids such as oil and water.