Refiners globally continue to face numerous challenges as environmental laws become increasingly stringent. Principal among them in the near future will be the International Maritime Organization’s (IMO) proposed changes to bunker fuel oil sulphur limits, from the current limit of over 3.5% down to 0.5% globally and from 1% to 0.1% in Emission Control Areas (ECA, see Figure 1). Global demand for high-sulphur residual fuel oil (HSFO) is steadily declining too, by 35% since 1995. Both of these changes will significantly impact a refiner’s ability to market any significant quantity of HSFO at a price that will maintain refinery profitability. Refineries currently making a significant amount of fuel oil and lacking the complexity to upgrade the resid- ual oil to premium products (middle distillates) will face two difficult options: either invest in commercially proven and reliable solutions to convert HSFO to more valuable liquid products such as Euro V diesel to greatly improve the refinery’s profitability, or face a threat to shut down the refinery as the operation becomes uneconomical to continue.