Explanation

The headquarters of OPEC is located in Vienna

OPEC stands for Organization of the Petroleum Exporting Countries.

It was founded on 14th September 1960 in Baghdad.

It consists of 13 members as of January 2020.

Its official language is English

Additional information:

OPEC had its headquarters in Geneva, Switzerland, in the first Five years of its existence 

This was moved to Vienna, Austria, on Sep 1, 1965