The density of dark Karo corn syrup is 1.37 grams per milliliter, while that of light Karo corn syrup is 1.33 grams per milliliter. Differences in density depend on the brand, type and grade of the corn syrup, which is rated by dextrose equivalence. Temperature and pressure also affect density.
Density is a measure of how much mass is in a given volume of matter. In corn syrup, as density increases, viscosity and sweetness also increase. The denser dark Karo corn syrup is more viscous and sweeter than light Karo corn syrup. Corn syrup is denser than water and oil. Therefore, when the three substances are mixed together, corn syrup rests at the bottom of the container.