To determine the exact role of various factors in silicone-oil emulsification, we investigated eight different silicone oils with specific physicochemical characteristics in terms of their rate of emulsification. The silicone oils were defined by viscosity, volatility, amount of low-molecular components, electrical resistivity, degree of purification and chemical composition. The viscosities differed between the ranges of 1000 and 10,000 cs. The silicone oils included purified polydimethylsiloxane (PDMS), hydroxyl-enriched PDMS and trimethylsiloxy-terminated polydiphenylsiloxane (PDPS). As emulsifiers we used 0.1% solutions of fibrinogen, fibrin, gamma globulins, acidic alpha-1-glycoprotein, very-low-density lipoprotein and serum dissolved in sterile, distilled water as well as in balanced salt solution. The group of low-viscosity silicone oils (1000 cs) was least stable. The greatest difference in stability was found among purified PDMS, having viscosities between 1000 and 5000 cs. The most stable oil was purified PDMS, whose emulsification rate was almost identical at 5000 and 10,000 cs. High contents of hydroxyl end groups enhanced silicone-oil emulsification to a greater extent than did phenyl side groups. The strongest emulsifiers were fibrinogen, fibrin and serum, followed by gamma globulins, very-low-density lipoprotein and acidic alpha-1-glycoprotein. Balanced salt solution accelerated silicone oil emulsification in all cases. For reduction of emulsification in vivo, purified PDMS of high viscosity should be used. Biologically active emulsifiers found in hemorrhages or inflammatory situations might be lowered in vivo by hemostasis and sufficient postoperative anti-inflammatory therapy.