Abstract: Metal working fluids being oil-in-water emulsions comprising alkylated polyvinylpyrrolidones as surfactants for emulsifying the oil in water. The alkylated polyvinyl-pyrrolidones having a molecular weight of about 1,000 up to 50,000 provide emulsions showing a high emulsion stability under varying and severe processing conditions of metal working fluids. Further, advantages of the metal working fluids are the narrow distribution of the droplet size, the high stability against varying temperature, the high stability against varying quality/composition of the make-up water, a high capacity of dispersing metal fines in the metal working fluid as well as excellent film forming characteristics.