  Quantum oscillations are conventionally understood to arise from the Fermi
level; hence, they are considered to be a proof of the existence of an
underlying Fermi surface. In this article, we show that in certain situations
quantum oscillations can also arise from inside the Fermi sea. We establish
this analytically, supporting it with numerical calculations. Possible
scenarios where such unusual behavior can occur are pointed out. In particular,
in strongly particle-hole asymmetric insulators, models of which have been
recently used in the context of the topological Kondo insulator SmB$_6$, we
show that the oscillations arise from inside the filled band, and are not
related to the gap.
