Where does most of the oil that pollutes the ocean come from?

When oil tankers operate carelessly, they can contaminate the marine environment with oil spills from loading and unloading operations at ports, intentional cleanups of their loading areas, accidents, and some sunken tankers.

New wells that are drilled can also lead to pollution if they are not done with enough caution. One of the worst accidents happened in the USA's South a few years ago (I won't name the company or location).

If old wells are not properly maintained, they also contribute to oil pollution.

According to the National Academy of Sciences, naturally occurring oil seeps beneath the surface of the Earth make up 60% of the estimated total load in North American waters and 40% globally.

https://tutor.hix.ai is the source.

Most of the oil that pollutes the ocean comes from land-based sources, such as oil spills from transportation, industrial activities, and urban runoff.