Abstract: Hydrocarbon oils having a high aromaticity (at least 85%, preferably 95-100%) and a boiling point of about 342.degree. to about 510.degree. C. (about 650.degree. to about 950.degree. F.) are used as partial or total replacements for the foam stabilizers used in the preparation of both rigid, closed cell polyurethane foams and flexible, open cell polyurethane foams. These oils are useful as a replacement for both silicon surfactants and organic (i.e., non-silicon) surfactants. For certain blowing agents (e.g., trichlorofluoromethane and methylene chloride), hydrocarbon oils having a boiling point range of about 399.degree. to 454.degree. C. (about 750.degree. to about 850.degree. F.) are preferred. Highly aromatic oils having a boiling point of about 281.degree. to about 510.degree. C. are useful for reducing the vapor pressure of toluene diisocyanate and for preventing the low temperature crystallization of toluene diisocyanate or diphenylmethane diisocyanate.