The collision of two barge convoys on the lower Mississippi River in February 2014 was far from a major casualty, but the litigation in its wake has helped answer a question that has loomed in US shipping law under the 1990 Oil Pollution Act (OPA 90).

The US Fifth Circuit Court of ­Appeals has ruled that Kentucky tug owner Marquette Transportation Co must contribute its share of the economic damages that Louisiana rival Settoon Towing has ­already paid for the oil spill ­because the US Coast Guard declared Settoon a “responsible party”.