THE HIGHLY COMPETITIVE COOLANT MARKET PROVIDES TODAY'S METALWORKING INDUSTRY WITH AN ARRAY OF FLUIDS FROM WHICH TO CHOOSE. THE USER CAN FIND THAT MAKING AN APPROPRIATE SELECTION CAN BE DIFFICULT. THE GENERAL APPROACH TO SELECTING A SUITABLE METALWORKING COOLANT IS SIMILAR WHETHER ONE IS CHOOSING A SOLUBLE OIL, SEMI- SYNTHETIC, OR SYNTHETIC. THIS PAPER DISCUSSES THE SELECTION AND USE OF SEMI-SYNTHETIC CUTTING FLUIDS, AND THEIR ADVANTAGES. TYPICAL PHYSICAL PROPERTIES, COOLANT CHEMICAL PROPERTIES, METHODS OF EVALUATING AND SELECTING A FLUID, AND THE PROPER MONITORING AND MAINTENANCE PROCEDURES FOR SEMI- SYNTHETIC COOLANTS ARE ALSO ADDRESSED.