  There is controversy as to whether a one-dimensional (1D) electron gas can
spin polarise in the absence of a magnetic field. Together with a simple model,
we present conductance measurements on ultra low-disorder quantum wires
supportive of a spin polarisation at B=0. A spin energy gap is indicated by the
presence of a feature in the range 0.5 - 0.7 X 2e^2/h in conductance data.
Importantly, it appears that the spin gap is not static but a function of the
electron density. Data obtained using a bias spectroscopy technique are
consistent with the spin gap widening further as the Fermi-level is increased.
