This prevents the heat of the oil from thawing the permafrost, and lets the caribou walk underneath. Oil used to be sold in barrels, which were transported by horse-drawn carts, and later by trucks. Offshore oil rigs are built over the sea. Oil may be loaded directly onto big ships called oil tankers, but sometimes pipelines are built to the offshore rigs. Then the pipeline is covered with concrete to stop it from bobbing up and down in the sea.
Crude oil includes some pretty heavy hydrocarbons, and a pipeline can get coated with wax.