Elastic means by increasing the price, the demand for that product decreases as well. For example when the price of lamb increases, people will shift to chicken. We say the demand for lamb is elastic.
Inelastic means, no matter how much the price changes, people still use it and the demand doesn't change a lot. Same as your example, Although the oil price increases, but the demand for oil didn'd decrease.
2-petrol is also sold from especialy designed petrol pumps which costly to buld and operate . in the other hand coke and soft carbonated drinks is sold everywhere and can be sold to anyway and any gae .patrol selling you must be an adult and hold a drivers licience . Gas in the long term has higher elasticity of demand. meaning since in short term people do not have much choice,so they consume whatever is available at whatever price.
3- the coke is advertosed on over hundered tv channels around the world and it is the best known trademark in the world is sold in about one hundred and...