Carbon Trading: The introduction of carbon (CO2) trading scheme has presented a new aspect of marginal mechanisms. Its essence is to set limitation on CO2 emission produced by industries. If a refinery can emit lower CO2 than the target value, then it can sell this credit to an over-producer, and gain additional revenue. Over-running from the target value means that the refinery must pay additional credit. Nowadays, carbon credit is traded in the open market, susceptible to price swings.