When do oil spills most frequently occur during marine transportation?

Oil spills most frequently occur during loading and unloading due to the significant risk associated with transferring oil from one location to another. During these operations, there is a potential for human error, equipment failure, or adherence to safety procedures to be compromised. Loading and unloading involve various steps that can lead to spillage, such as overfilling tanks, equipment leaks, or issues with the connection between hoses and ports.

In contrast, spills may also occur at sea but are generally less frequent than those during the transfer process, where the potential for accidents is heightened. Storage tanks can also contribute to spills, but these are typically considered maintenance issues and not operational spills related to transportation. Refueling operations, while risky, tend to be controlled and regulated, further reducing the likelihood of spills compared to the loading and unloading phases.