Density and Viscosity: Causes and Effects

[scientifico]

Hello, what forces causes density and viscosity in a fluid ?
I thought oil was more dense than water but it is only more viscous. I suppose a very viscous liquid has strong forces interacting between the molecules so they became closer and shouldn't density increase too ?

Thank you

 

[mathman]

This is not a complete answer. However, oil (CH₂) is intrinsically lighter than water (H₂O). Also oil molecules consist of long chains, while water molecules are individual.

http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Viscosity-840.html