  We study a sample of six X-ray selected broad absorption line (BAL)
quasi-stellar objects (QSOs) from the XMM-Newton Wide Angle Survey. All six
objects are classified as BALQSOs using the classic balnicity index, and
together they form the largest sample of X-ray selected BALQSOs. We find
evidence for absorption in the X-ray spectra of all six objects. An ionized
absorption model applied to an X-ray spectral shape that would be typical for
non-BAL QSOs (a power law with energy index alpha=0.98) provides acceptable
fits to the X-ray spectra of all six objects. The optical to X-ray spectral
indices, alpha_OX, of the X-ray selected BALQSOs, have a mean value of 1.69 +-
0.05, which is similar to that found for X-ray selected and optically selected
non-BAL QSOs of similar ultraviolet luminosity. In contrast, optically-selected
BALQSOs typically have much larger alpha_OX and so are characterised as being
X-ray weak. The results imply that X-ray selection yields intrinsically X-ray
bright BALQSOs, but their X-ray spectra are absorbed by a similar degree to
that seen in optically-selected BALQSO samples; X-ray absorption appears to be
ubiquitous in BALQSOs, but X-ray weakness is not. We argue that BALQSOs sit at
one end of a spectrum of X-ray absorption properties in QSOs related to the
degree of ultraviolet absorption in C IV 1550.
