Research shows that microorganisms play a significant role in corrosion of buried steel pipes. Partially hydrolyzed polyacrylamide (HPAM), a polymer commonly used to enhance oil recovery (EOR) from reservoirs, has been found to benefit microorganisms as a nutrient source, resulting in severe microbial corrosion of steel in the vicinity. Herein, microbial corrosion behavior of carbon steel was examined under active Fe oxide and inert sand deposits in oilfield water containing HPAM and sulfate-reducing bacteria (SRB). The electrochemical results show that corrosion rate of the steel under the Fe oxide deposit was generally higher than that under the sand deposit. The steel under the Fe oxide deposit suffered severe pitting assault with wider and deeper pits of about 32.65 µm. In comparison, corrosion severity decreased in the sand-deposited sample (having a maximum pit depth of 11.22 µm). The results demonstrate a synergistic effect between SRB activities and Fe oxide deposits to exacerbate steel corrosion in the oilfield water containing HPAM gel.