  The superconducting phase diagram of MgB2 was determined from magnetization,
magneto-transport and the first single-crystal specific heat measurements. A
zero-temperature in-plane coherence length of 8 nm is determined. The
superconducting anisotropy increases from a value around 2 near Tc to above 4.5
at 22 K. For H||c a pronounced peak effect in the critical current occurs at
the upper critical field. Evidence for a surface superconducting state is
presented for H||c which might account for the wide spread in reported values
of the anisotropy.
