The results of the Granger causality tests show that in the long-run there was a one direction
relationship between petroleum price and the prices of each of the four vegetable oils, i.e., palm, rapeseed, soyabean and sunflower oils. The reverse was not true, i.e., petroleum price was not influenced by the price of any of the vegetable oils under study. These results suggest that petroleum price is a factor growing in significance in the vegetable oils complex. In the past, petroleum used to enter the aggregate production function of the agricultural commodities through the use of various energy-intensive inputs (such as fertilizer and fuel for agricultural commodities), as well as for transportation. However, lately, the high price of petroleum has boosted the demand for biofuels such as biodiesel which utilizes vegetable oils as feedstocks. Clearly, further analysis on the workings of the vegetable oil markets will have to incorporate petroleum price as one of the major market determinants as well as an influence on the structural and behavioural aspects of the markets. The results of this study differ from those obtained by �Y et al. (2006), most probably due to the differences in the adopted techniques, data frequency and time span, which lend support to Hakkio and �ush’s (1991) argument that increasing the number of observations does not add any robustness to the results in tests of co-integration, and that the time span is more important. Another difference is that our study used more recent data.