This study examines the relationship between crude oil ans petroleum products prices in the European, Asian and North American markets. We develop an econometric model, based on the long term equilibrium between the prices, which takes into account the changes in the oil product demand trends. We explain price behaviors by the impact of the demand trends. Because the refining industry which transforms crude into petroleum products is a joint product industry, petroleum product pricing is affected by demand trends both in terms of quality and quantity. Consequently, the long term equilibrium between prices, estimated through a cointegration approach, are affected by several structural breaks. We also develop a panel econometric model which simultaneously takes into account the relative prices of all world products towards one crude. Finally, the different results are compared to the marginal costs derived from an oil refining optimization model. This econometric modeling approach enables a better understanding of the long terme equilibrium between prices of petroleum products and crude.