Monoaryloxide-pyrrolide (MAP) olefin metathesis catalysts of molybdenum that contain a chiral bitetralin-based aryloxide ligand are efficient for ethenolysis of methyl oleate, cyclooctene, and cyclopentene. Ethenolysis of 5000 equiv of methyl oleate produced 1-decene (1D) and methyl-9-decenoate (M9D) with a selectivity of > 99%, yields up to 95%, and a TON (turnover number) of 4750 in 15 h. Tungstacyclobutane catalysts gave yields approximately half those of molybdenum catalysts, either at room temperature or at 50 degrees C, although selectivity was still > 99%. Ethenolysis of 30000 equiv of cyclooctene to 1,9-decadiene could be carried out with a TON of 22 500 at 20 atm (75% yield), while ethenolysis of 10000 equiv of cyclopentene to 1,6-heptadiene could be carried out with a TON of 5800 at 20 atm (58% yield). There is no reason to propose that the efficiency of ethenolysis has been maximized with the most successful catalyst reported here.