The Organization of the Petroleum Exporting Countries (OPEC) said Friday that its basket oil price plummeted 4.15 dollars the previous day. OPEC\'s oil on Thursday tracked the fall of international benchmark crude oil brands with a delay of one day and settled at 107.20 dollars per barrel (159 litres). Analysts said markets were reacting to indications that recent high prices are leading to a decrease in demand. Higher interest rates in China and Greece\'s financial troubles added to the negative sentiment, consultants at JBC Energy said in Vienna.