Chemical reaction fouling in petrochemical units such as separators, heat exchangers, pumps and compressors is a serious and costly problem. Autoxidation has been identified as a prime source of deposit formation in oxygenated process streams and fuel storage systems but the fouling mechanism has not been fully understood. The objective of this study is to investigate the mechanisms involved in autoxidation fouling. Blended naphtha (a mixture of refinery naphtha and an internal recycled stream) was used as the test fluid in batch experiments.