  We present a sample of 242 ultra-short-period (P < 0.22 d) eclipsing and
ellipsoidal binary stars identified in the OGLE fields toward the Galactic
bulge. Based on the light curve morphology, we divide the sample into
candidates for contact binaries and non-contact binaries. In the latter group
we distinguish binary systems consisting of a cool main-sequence star and a
B-type subdwarf (HW Vir stars) and candidates for cataclysmic variables,
including five eclipsing dwarf novae. One of the detected eclipsing binary
systems - OGLE-BLG-ECL-000066 - with the orbital period below 0.1 d, likely
consists of M dwarfs in a nearly contact configuration. If confirmed, this
would be the shortest-period M-dwarf binary system currently known. We discuss
possible evolutionary mechanisms that could lead to the orbital period below
0.1 d in an M-dwarf binary.
