The U.S. National Bureau of Standards established the Baumé scale (degrees Baumé) as the standard for measuring specific gravity, or density of liquids less dense than water. API gravity, is a measure of how heavy or light a petroleum liquid is compared to water.
Not density. Weight as compared to the heavier weight of water. Density is varied by temperature. Weight is not. We still do not know the temperature of the oil. If it is very low, then its weight would be a more accurate metric. Not its volume at an undefined temperature.
The oil’s temperature will be the same as the surrounding water. If you know the temperature of the ocean water, you know the temperature of the oil.
The oil’s weight will not vary with temperature.
Its density relative to water is the best measure of whether it will sink or float. Assuming the oil and water are at the same temperature, which they are, then the relative gravity will tell you that.