For the years 1971 to 1989 the data source is
World Bank.
For the years 1990 to 1993 the data source is
IEA.
For the years 1998 to 1999 the data source is
IEA.
For the years 2001 to 2014 the data source is
IEA.
For the years 2015 to 2022 the data source is
Ember.