VIENNA, April 28 (Xinhua) -- The Organization of the Petroleum Exporting Countries (OPEC) daily basket price dropped to 13.30 U.S. dollars a barrel on Monday, compared with 14.31 dollars last Friday, according to OPEC Secretariat calculations released on Tuesday.

Oil tank train cars sit idle Tuesday, April 21, 2020, in East Chicago. (File photo: AP)

Also known as the OPEC reference basket of crude oil, the OPEC basket, a weighted average of oil prices from different OPEC members around the world, is used as an important benchmark for crude oil prices.

It currently averages the oil prices of 13 countries, namely Algeria, Angola, the Republic of the Congo, Equatorial Guinea, Gabon, Iran, Iraq, Kuwait, Libya, Nigeria, Saudi Arabia, the United Arab Emirates and Venezuela.