A method for treating a substrate prior to a metathesis reaction includes treating the substrate with a first agent configured to mitigate potentially adverse effects of one or more contaminants in the substrate on a catalyst used to catalyze the metathesis reaction. The treating reduces a level of the one or more contaminants by an amount sufficient to enable the metathesis reaction to proceed at a substrate-to-catalyst molar ratio of at least about 7,500 to 1. Methods for metathesizing substrates are described.