An investigation was undertaken of commercially feasible methods of improving the durability of asphalt roofing shingles in the harsh environment of the southern United States. Two methods of investigation were used: Weather-Ometer exposures of coating asphalts and outdoor exposures of duplicate Weather-Ometer panels. New techniques were introduced to investigate degradation including optical microscopy and scanning electron microscopy (SEM). Systems investigated included four kinds of stabilizers and two asphalts. Identical test panels were exposed in the Weather-Ometer and outdoors in Tampa, Florida, yielding a tentative correlation between them. Controlled experimentation was supplemented by field inspections of actual roofs for periods ranging from 1 to 20 years, these exposures yielding evidence of correlation with the Weather-Ometer. Results of these investigations provided a basis for selecting one stabilizer as significantly better than all others.