These are hydrocarbon fuel chains. The black circles are carbons, the paie blue are hydrogen.

...2b. More (click here) on relating the physical properties of the hydrocarbon fractions to their uses and dangers...

The hydrocarbon chains to the left are the result of the distillation process below. 

From above, "As the hydrocarbon molecule gets bigger, the surface to surface contact increase...Hence, the increase in viscosity, melting points and boiling points...