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 year 1994 the data source is
EIA.
For the year 1995 the data source is
IEA.
For the years 1996 to 1999 the data source is
EIA.
For the years 2000 to 2022 the data source is
Ember.