High-temperature corrosion from low melting ash deposits, low-temperature corrosion, and low-temperature deposits produced by condensed sulfuric acid are three potential problems associated with residual fuel oil firing in steam generators. This paper discusses test work carried out on a large unit type steam generator in an effort to alleviate these problems through low-excess air operation and the use of a magnesium additive. Results indicate that these two steps are of significant help.