Harsh physical and chemical environments found in downhole operations have traditionally required the use of exotic corrosion-resistant materials, which are expensive, difficult to source and challenging to machine. This paper evaluates high-phosphorous electroless nickel (EN) coating as an alternative to these materials. The performance of this coating on carbon steel is compared to the performance of corrosion resistant alloys for fouling and surface characterization, and adhesion of inorganic and organic materials in a series of laboratory and field tests. In this paper, we first describe the complex and hostile thermal-chemical environment that exists for well completions commonly used in oil and gas production. The chemistry, physics and engineering governing principles of corrosion and fouling are reviewed. The set-up of the laboratory facilities and test procedures for fouling are described in detail. The performance of EN coated carbon steel is compared to several corrosion resistant alloys commonly used in downhole operations: 13Cr-L80, 28Cr-L80, 316L stainless steel, and Inconel 625. Examination of these specimens indicates the extent of corrosion and accumulation of fouling substances on EN coated and uncoated carbon steel at each time point.