High-density polyethylene (HDPE) sample tanks manufactured by using a rotational molding process were used in a study to determine the presence and characteristics of antioxidants at the inside and outside surfaces of the tanks. The sample tanks were manufactured by using three different processing times to create undercooked, ideal, and overcooked tanks. Differential scanning calorimetry (DSC) was used to perform oxidation induction time (OIT) studies by using specimens cut from the surfaces of the tank. The OIT portion of the analysis exposes the melted HDPE specimens to an oxygen environment at 200degreesC for over 2 h. The DSC monitors change in the energy transfer rate to or from the specimen because of chemical reactions. A numerical integration process was used to analyze the DSC-OIT data and to obtain additional information about the energy levels measured during the analysis. Fourier transform infrared (FTIR) studies were also performed to determine the chemical characteristics of specimens cut from the processed tanks. Results showed increased degradation at the inside surfaces of the overcooked tanks because of a lack of antioxidants. The results also showed that metal ions from the mold wall could react with the outside surfaces of the tanks and influence the level of antioxidants at that surface. (C) 2004 Wiley Periodicals, Inc.