On June 15, 2005 the OPEC basket was changed to reflect the characteristics of the oil produced by OPEC members. The Reference Basket currently consists of a weighted average of the following blends of oil:
OPEC attempts to keep the price of the Opec Basket between upper and lower limits, by increasing and decreasing production. This makes the measure important for market analysts. The OPEC Basket, including a mix of light and heavy crudes, is heavier than both Brent crude oil, and West Texas Intermediate crude oil.