For the years 1980 to 1984 the data source is
EIA.
For the years 1985 to 1987 the data sources are
EIA
and
IEA (imports/exports).
For the years 1988 to 1989 the data source is
EIA.
For the years 1990 to 2014 the data source is
IEA.
For the years 2015 to 2021 the data source is
Ember.