Yes, very. Because of the tedious process and shipment it causes the price to increase.
Dearer means costly...
They are locked in shale rock.
The compressor will seize. They are very costly to replace.
Some essential oils are readily available and reasonably priced, others are more difficult to find and/or much more costly. Depending on which oils you are looking for, if you are looking for an essential oil, do not purchase a fragrance oil and expect the same results.
You will burn the motor up, which will be a very costly repair.
Yes. Canola oil is an edible cooking oil processed from Canadian wheat. Perfectly safe, but costly to burn as fuel.
Assuming you mean oil as in the petroleum product? yes. Oil spills and oil tanker wrecks are devastating to all forms of sea life that are in their proximity. Oil cleanup from water is possible, but it is difficult, costly, and only somewhat effective at removing pollutants.
There is no better oil. Each oil has more or less benefits depending on your situation. Like anything you get what you pay for, cheaper oils have less costly additives that keep your engine clean and wear to a minimum.
The superlative for costly is "most costly" or "costliest."
Yes, whale oil was mostly used to light the lanterns in the colonies. The lanterns were not used in all homes because the oil was costly. Many homes only used the fireplace as a source of light.
Yes, costly is an adjective. E.g. It was a costly mistake. (One that was expensive to fix, or that led to other bad consequences.)
Costly.