Major changes are unfolding that will impact the marine shipping industry. Within the next decade, tighter environmental rules will be in place, changing fuels used to propel international and domestic vessels. These new environmental rules were developed by the International Maritime Organization and are commonly referred to as MARPOL.1 Under MARPOL, the sulfur (S) content of marine fuel oil is being decreased. In January 2012, the S content of marine fuels was lowered from 4.5 wt% to 3.5 wt%. More importantly, beginning in January 2020, the S content of marine fuels will drop to 0.5 wt% (5,000 ppm S). Marine fuels, commonly grouped under heavy fuel oil (HFO), were the final refined product in which refiners could effectively move S-containing compounds from other clean transportation fuels.