IN A PROCESS FOR FORMING SULFURIZED POLYBUTENES FOR USE IN METAL WORKING OILS INCLUDING REACTING MOLTEN SULFUR WITH LOW MOLECULAR WEIGHT POLYBUTENES, STRIPPING TO REMOVE LIGHT UNDERIRABLE COMPONENTS SUCH AS HYDROGEN SULFIDE, VARIOUS MERCAPTANS AND UNREACTED POLYBUTENES, REMOVING ENTRAINED SULFUR AND COOLING TO AMBIENT CONDITIONS, THE IMPROVEMENT WHICH COMPRISES ENHANCING THE RETENTION OF CHEMICALLY COMBINED SULFUR IN SUCH POLYBUTENES BY MAINTAINING THE PH IN THE RANGE OF ABOUT 2.0 TO 5.5 FOR A PERIOD OF TIME SUFFICIENT TO SUBSTANTIALLY STABILIZE THE CHEMICALLY COMBINED SULFUR CONTENT OF THE SULFURIZED POLYBUTENES. SUITABLY, THE PH IS MAINTAINED WITHIN THE RANGE SET FORTH FROM AFTER THE STRIPPING STEP UNTIL AT LEAST THE AMBIENT CONDITIONS ARE REACHED. CONTINUED MAINTENANCE OF THE PH DURING STORAGE IS ALSO DESIRABLE.