An observer noticed a large oil tanker parked at an oil terminal for 2 days. On the second day more of the hull of the ship was visible. Was the tanker picking up oil or delivering it?

A ship with a cargo rides lower in the water than when it has no cargo.

As the cargo is unloaded, the ship rises in the water, revealing parts of the hull which had been below the water level.

What the observer was looking at was a ship which was in the process of delivering its oil to the terminal.