Hydrocarbon fluids are produced by hydrocracking a vacuum gas oil stream, fractionating and/or hydrogenating the hydrocracked vacuum gas oil. The fluids typically have ASTM D86 boiling point ranges within the range 100.degree. C. to 400.degree. C. the range being no more than 75.degree. C., they also have a naphthenic content greater than 60%, the naphthenics containing polycyclic materials, an aromatic content below 2% and an aniline point below 100.degree. C. The fluids are particularly useful as solvents, for printing inks, drilling fluids, metal working fluids and as silicone extenders.