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By applying two nonlinear Granger causality testing methods and rolling window strat-egy to explore the relationship between speculative activities and crude oil prices,the unidirectionalGranger causality from speculative activities to returns of crude oil prices during the high price phase isdiscovered.It is proved that speculative activities did contribute to high crude oil prices after the Asianfinancial crisis and OPEC’s output cut in 1998.The unidirectional Granger causality from returns ofcrude oil prices to speculative activities is significant in general.But after 2000,with the sharp rise incrude oil prices,this unidirectional Granger causality became a complex nonlinear relationship,whichcannot be detected by any linear Granger causality test.
By applying two nonlinear Granger causality testing methods and rolling window strat-egy to explore the relationship between speculative activities and crude oil prices, the unidirectional Granger causality from speculative activities to returns of crude oil prices during the high price phase isdiscovered. It is verified that speculative activities did contribute to high crude oil prices after the Asian financial crisis and OPEC’s output cut in 1998. The unidirectional Granger causality from returns of crude oil prices to speculative activities is significant in general.But after 2000, with the sharp rise incrude oil prices, this unidirectional Granger causality has a complex nonlinear relationship, whichcannot be detected by any linear Granger causality test.