Theoretically according to the gold/oil ratio, gold investing years might include any year when the gold/oil ratio dipped below 15, that is, when the price of oil was more expensive, making an ounce of gold "cheaper" than 15 barrels of oil, say 9 barrels instead of 15 as in 2005 and 2008:
1981 13.13
1982 11.91
1983 14.63
1984 13.11
1985 11.97
2000 10.19
2001 11.78 (gold $271.04/ounce, lowest average annual price for gold since 1980 to date)
2002 13.58
2003 13.12
2004 10.95
2005 8.91 (gold $444.74/ounce)
2006 10.35
2007 10.83
2008 9.53.
Not coincidentally, Vanguard launched both its energy fund, VGENX, and its precious metals fund, VGPMX, on May 23, 1984 when it was time to invest in gold and avoid oil. But if you had invested $10,000 in the energy fund that year, by May 31, 2008 you'd have in excess of $352,000. The precious metals fund did much less well, almost reaching $107,000 over the same period.