Many of these models have been criticized for being unreliable, since most of the evidence presented to support the assumption that commodity prices were cointegrated was flawed and affected by spurious regressions, nonstationary1 series, or inappropriate use of first differences (Ardeni, 1989). In order to deal with these econometric shortcomings, Engel and Granger (1987) proposed a new and alternative methodological approach based on cointegration theory, which indicates that two nonstationary time senes could be long-term cointegrated if both series are integrated of the same order.