  Energy spectrum of biased bilayer graphene near the bottom has a
"Mexican-hat"-like shape. For the Fermi level within the Mexican hat we predict
that, apart from conventional magnetooscillations which vanish with
temperature, there are additional magnetooscillations which are weakly
sensitive to temperature. These oscillations are also insensitive to a
long-range disorder. Their period in magnetic field scales with bias, V, as
V^2. The origin of these oscillations is the disorder-induced scattering
between electron-like and hole-like Fermi-surfaces, specific for Mexican hat.
