  We performed de Haas-van Alphen (dHvA) experiments in the spin-triplet
superconductor UTe2 for magnetic field along the c-axis above 15T. Three
fundamental dHvA frequencies, named alpha1, alpha2 and beta corresponding to
the cross sections of cylindrical Fermi surfaces (FSs) with large cyclotron
effective masses (33-43 m0) were detected. No other fundamental dHvA
frequencies were detected at high frequency range, suggesting a
cylindrical-shaped electron FS without connecting at the Z point of the
Brillouin zone. However, the existence of small pocket FSs associated with
extremely heavy masses cannot be fully excluded.
