time, in most OB stars with well developed but unsaturated wind lines. For example, a preliminary examination of the 106 B0-B5 supergiant sample analysed by Prinja et al. (2005) indicates that NACs are evident in $\sim$70[%]{} of the stars which exhibit well-developed, unsaturated P Cygni profiles in either Si[iv]{} or C[iv]{}.

[llll]{} & & &\
\
HD 13866 & B2 Ib-II:p & 18.1 & 0.44\
HD 47240 & B1 Ib & 21.7 & 0.50\
HD 111990 & B2 Ib & 18.1 & 0.37\
HD 51309 & B3 Ib & 17.5 & 0.38\
HD 36371 & B4 Ib & 17.4 & 0.22\
AV 264 & B1 Ia & 22.5 & 0.38\
\
HD 91316 & B1 Iab & 21.9 & 0.57\
HD 191877 & B1 Ib & 21.7 & 0.55\
HD 93840 & BN1 Ib & 21.7 & 0.55\
HD 100276 & B0.5 Ib & 25.4 & 0.65\
HD 152234 & B0.5 Ia & 24.7 & 0.66\
HD 224151 & B0.5 II & 27.5 & 0.66\

The special case of NACs in decoupled Si[iv]{} $\lambda\lambda$1394,1403 lines
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The general problem with measuring mass-loss rates from UV wind lines is that the wind line variability we see is due to structures in 