  Fast rotation of compact stars (at submillisecond period) and, in particular,
their stability, are sensitive to the equation of state (EOS) of dense matter.
Recent observations of XTE J1739-285 suggest that it contains a neutron star
rotating at 1122 Hz (Kaaret et al. 2007). At such rotational frequency the
effects of rotation on star's structure are significant. We study the interplay
of fast rotation, EOS and gravitational mass of a submillisecond pulsar. We
discuss the EOS dependence of spin-up to a submillisecond period, via mass
accretion from a disk in a low-mass X-ray binary.
