The title compound, [Mo(C5H5)(C3H9P)(CO)(3)]BF4, forms by a ligand-redistribution reaction from [(eta(5)-C5H5)Mo(CO)(2)(PMe3)FBF3], which is produced at low temperature by protonation of [(eta(5)-C5H5)Mo(Co)(2)(PMe3)H] with HBF4. The cation has a typical four-legged piano-stool geometry, with Mo-P 2.496 (2) and Mo-Cnt 2.00 (2) Angstrom, where Cnt is the centre of gravity of the cyclopentadienyl ring.