Marathon Petroleum is investing extra resources in its largest US refinery to boost production of low-sulphur marine fuel ahead of the pending switch in 2020.

The company's largest US refinery, Garyville in Louisiana, is undertaking a $207m project to increase its coking capacity. Cokers can turn high-sulphur residual fuel into lighter products.

Along with the Garyville project, Marathon says it is working on reconfiguring its Galveston Bay refinery to produce more low-sulphur fuel.