This paper is aimed to examine and understand the feasibility of replacing dimethyl disulfide (DMDS) with disulfide oil (DSO) in olefin units of the Amir Kabir Petrochemical Refinery (Khuzestan, Iran). This substitution not only provides a very low-priced supply for replacing DMDS in olefin plants, but also it restrains emitting poisonous sulfur gas to the environment. Considering the fact that the conversion of DSO to hydrogen sulfide required a longer residence time related to DMDS, the DSO pilot was built to examine this alteration. Comparing the results with those of DMDS revealed that this pilot allowed for complete replacement. The polynuclear aromatics mechanism was the predominant mechanism, and optimization results showed that three selected parameters (temperature, retention time, and DSO injection rate) affected the CO production. The rate of CO formation was very similar for using both cases. The total sulfur content, which is an environmental pollutant and a component of gasoline, was also controlled. With DMDS, the total sulfur content varied from 20 to 130 ppm, while with DSO it varied from 20 to 100 ppm, which was acceptable. As a result of this process, approximately 221 000 EUR would be saved per year in an olefin unit with an ethylene production capacity of 520 000 tons.