If there is an increase in price of petrol, there would be a movement along the demand curve and a smaller quantity would be bought.
Liquidated Damages: These types of damages are awarded when there is a provision in a contract which states the amount of damages that shall be awarded in the event of a breach. Liquidated damages cannot be used as punishment to a party or to harm the party for the breach.
In most cases of breach, a party to the contract simply fails to perform one or more terms. In those cases, the breaching party should have already considered the cost to perform those terms and thus keeps that cost when they do not perform. That party should not be entitled to keep that savings.