Peng Liu; Ke Tang
Abstract: This paper finds that the long-term co-movement of commodity prices is driven by economic relationships, such as production, substitution, and complementary relationships. Such relationships imply that the convenience yield of a given commodity depends on its relative scarcity with respect to associated commodities. The economic linkage between two commodities creates a new source of positive correlation between the futures returns of both commodities. We build an empirical, multi-commodity maximal affine model that allows the convenience yield of a commodity to depend on its relative scarcity. We estimate the model using three commodity pairs: heating oil-crude oil, WTI-Brent crude oil and heating oil-gasoline. Our model allows for a flexible correlation term structure of futures returns that matches the upward-sloping patterns observed in the data. The high long-term correlation implied by an economic relationship reduces the volatility of the spread between commodities, which implies lower spread option prices. An out-of-sample test using short-maturity crack spread options data shows that our model considerably reduces the negative bias generated by traditional models.