Hi Dewasish,
As of now I have seen that Spread works with these Commodities very well (I keep on doing the backtesting of various commodities & cross commodities for Spread strategy):
Gold, Silver, Copper, Zinc, Lead & Zinc
(As I don't trade in Agri Commodities........... So I have never tested it.)
To know the degree of correlation between the two commodities in excel, put the formula:
= CORREL(Commodity 1, Commodity 2)
It determine whether two Commodity sets are related, and if so, how strongly. The correlation coefficient ranges from +1, indicating a perfect positive linear relationship, to -1, indicating a perfectly negative linear relationship.