The US National Transportation Safety Board (NTSB) placed primary blame on a Houston pilot for a March 2015 collision that led to a spill.
But it also called for better procedures to manage shipping traffic in the Houston Ship Channel during dense fog.
The agency said the pilot faced handling difficulties on the 57,100-dwt bulker Conti Peridot (built 2011), which collided with Maersk Tankers' 45,000-dwt chemical tanker Carla Maersk (built 1999).
