The purpose of opec, the organization of petroleum exporting countries, is to

The purpose of Opec is to stabilize the price of oil and ensure a regular supply of oil to other countries.
In order to do this, each oil suppliers that became the member of OPEC will put a similar price on the oil products they sell to other countries and put a maximum quota on how much oil each member could sell within an accounting period.

It should be at the center of any map going vertically: the prime meridian, as it passes through greenwich,  england, is considered 0 degrees longitude