  We investigate the structure and X-ray emission from the colliding stellar
winds in massive star binaries. We find that the opening angle of the contact
discontinuity (CD) is overestimated by several formulae in the literature at
very small values of the wind momentum ratio. We find also that the shocks in
the primary (dominant) and secondary winds flare by approx 20 degrees compared
to the CD, and that the entire secondary wind is shocked when the wind momentum
ratio < 0.02. Analytical expressions for the opening angles of the shocks, and
the fraction of each wind that is shocked, are provided. We find that the X-ray
luminosity scales with the wind momentum ratio, and that the spectrum softens
slightly as the wind momentum ratio decreases.
