The boiling point increases as the number of carbon atoms (chain length) increases.

The viscosity increases as the number of carbon atoms (chain length) increases.

The viscosity of a fluid describes how easily it flows. Water has a low viscosity, it flows very easily. Crude oil has a higher viscosity than water, it does not flow very easily.

Fractions (in order)Properties
Refinery gasesSmallest molecules. Lowest boiling point. Lowest viscosity.
Gasoline
Kerosene
Diesel
Fuel oil
BitumenLargest molecules. Highest boiling point. Highest viscosity.