Deposition in flow lines and processing and heat transfer equipment arises from fouling species, which may either be present in the fluid or generated in the vicinity of the equipment surface. Recent research on deposition during heat transfer from petroleum feedstocks is reviewed. For low-sulfur light crude oils, deposition is largely due to particulates and gums. For medium-sulfur crude oils, the formation of iron sulfides plays a major role in deposition. In unstable heavy oil systems, suspended asphaltenes are the fouling species. Trace quantities of impurities such as dissolved oxygen or suspended corrosion products add markedly to deposit formation. The influences of flow velocity, bulk and surface temperatures, and particulate concentrations are demonstrated through experimental results and compared to expectations from simple models. Through an understanding of the key steps in the deposition processes, a rational mitigation strategy can be formulated.