||Deep boreholes in polar ice sheets have to be filled with a liquid in order to prevent hole closure due to the overburden pressure of the ice. In Greenland, at ice temperatures of -32oC, the limit for open hole drilling is 400m. In Antarctica, a depth of 900m has been obtained in an open hole. All drilling to deeper depths needs to be performed in a liquid. The borehole liquid should have a density close to that of ice, be non-toxic, available in quantities at reasonable cost, compatible with the materials in the drill, non-aggressive to ice, and have a low viscosity to allow rapid drill movement in the borehole. In practice, no liquid has been available that can fulfill all the requirements. In the past, ethanol/water mixture, DFA/Glycol, DFA/TCE, JET-A1/PCE, DFA/F113,nbutyl acetate, and D60/F113 have been used. All liquids have their own advantages and disadvantages, and the use of all have involved severe compromises. In this paper, these ideal specifications are compared to those of the actually used hole liquids.