I found a list of historic petrol prices in Australia going back to 1925.
https://www.bitre.gov.au/sites/default/files/is_082.pdf (second last page)
Keep in mind it is in nominal dollars, it does not account for inflation. There is a CPI deflator in there if you wish to convert it to current dollars. (Edit: The CPI deflator is in 2011 dollars. You need two jumps to get to 2020. For example, 1974>2011. 2011 > 2020). For example, the price of fuel of 12.1c in 1974 is approximately 84c/l in 2020. But also keep in mind that excludes changes in fuel excise etc.
Year c/l
1926 5.00
1927 4.65
1928 4.30
1929 4.20
1930 4.05
1931 4.00
1932 4.00
1933 4.00
1934 3.95
1935 3.85
1936 3.80
1937 3.85
1938 3.90
1939 3.95
1940 4.75
1941 5.50
1942 5.85
1943 6.20
1944 6.20
1945 6.06
1946 5.77
1947 5.27
1948 5.59
1949 5.96
1950 6.43
1951 6.82
1952 7.40
1953 7.78
1954 7.31
1955 7.20
1956 7.68
1957 8.26
1958 8.05
1959 7.87
1960 7.79
1961 7.72
1962 7.48
1963 7.53
1964 7.43
1965 7.41
1966 7.99
1967 8.17
1968 8.52
1969 8.56
1970 8.73
1971 9.53
1972 10.1
1973 10.1
1974 12.1
1975 14.0
1976 16.1
1977 16.9
1978 18.3
1979 22.5
1980 30.6
1981 33.7
1982 35.9
1983 41.9
1984 46.0
1985 49.7
1986 52.5
1987 53.9
1988 54.7
1989 52.6
1990 60.3
1991 69.4
1992 66.7
1993 68.1
1994 67.0
1995 67.6
1996 70.6
1997 72.0
1998 70.6
1999 67.0
2000 78.2
2001 91.7
2002 83.8
2003 89.0
2004 91.2
2005 101.
2006 121.
2007 122.
2008 135.
2009 127.
2010 124.
2011 132.
2012 143.
2013 142.
2014 150.
2015 133.
2016 122.