  We have investigated the effect of an in plane parallel magnetic field (B_||)
on two high mobility metallic-like dilute two-dimensional hole gas (2DHG)
systems in GaAs quantum wells. The experiments reveal that, while suppressing
the magnitude of the low temperature resistance drop, B_|| does not affect E_a,
the characteristic energy scale of the metallic resistance drop. The field B_c
at which the metallic-like resistance drop vanishes is dependent on both the
width of quantum well and the orientation of B_||. It is unexpected that E_a is
unaffected by B_|| up to Bc depite that the Zeeman energy at B_c is roughly
equal to E_a.
