Which group had been an example for successfully determining the amount and price of a world-wide commodity

Organization of Petroleum Exporting Countries

Explanation:

Probably more known as OPEC.

This group consist of 14 nations that possess the largest oil reserves in the world. They regularly held meetings to discuss how they should supply the oil product in order to maintain  control of the oil market.

What they do is ensuring their members to not over distribute their oil to the market. This will make the oil maintain a constant state of scarcity and keep the demand of the product really high in the Global market. They've been really successful at it for more than 5 decades.