expanding on Lorax's mention of hedging- commodity producers generally hedge their output... so you have a few factors at play here that can cause a producer's price to deviate substantially from the price of the underlying product: 1. what's in their hedge portfolio? could have optionality, irregular expiries, quantities, exotic features, etc that are not at all linear 2. if they hedge their production bilaterally, who are their counterparties? what is their credit worthiness and how could that be fluctuating (a mild influence, but present) 3. they have a production forecast that's potentially irregular based on new sources coming to market, expired ones depleting, grade differences, etc 4. they have costs, cash flows and internal risks as a company that are also irregular and weight against their value as a stock