Year	billion cubic meters
1961	21
1962	21
1963	21
1964	21
1965	21
1966	21
1967	21
1968	21
1969	21
1970	21
1971	21
1972	21
1973	21
1974	21
1975	21
1976	21
1977	21
1978	21
1979	21
1980	21
1981	21
1982	21
1983	21
1984	21
1985	21
1986	21
1987	21
1988	21
1989	21
1990	21
1991	21
1992	21
1993	21
1994	21
1995	21
1996	21
1997	21
1998	21
1999	21
2000	21
2001	21
2002	21
2003	21
2004	21
2005	21
2006	21
2007	21
2008	21
2009	21
2010	21
2011	21
2012	21
2013	21
2014	21
2015	21
2016	21
2017	21
2018	21
2019	21
2020	21