  We present Arecibo 21 cm spectroscopy, Keck HIRES Hb spectroscopy, and WIYN
R-band images of 11 nearby blue compact galaxies selected to be similar to blue
compact star-forming galaxies at intermediate redshifts (0.1<z<1). We detect HI
in 10 of 11 sample galaxies, yielding HI masses of 0.3-4x10^9 M_odot, HI
linewidths, W_20, of 133-249 km/s, dynamical masses of 0.5-5x10^10 M_odot, gas
depletion timescales, tau_gas, of 0.3-7 Gyr, HI mass fractions of 0.01-0.58,
and mass-to-light ratios of 0.1-0.8. These values span the range typical of
nearby HII galaxies, irregulars and spirals. Despite the restricted
morphological selection, our sample is quite heterogeneous in HI content,
dynamical mass, and gas depletion timescale. Therefore, these galaxies should
look very different from each other in 5 Gyr. Fading of intermediate-z luminous
blue compact galaxies into NGC-type spheroidals is a viable evolutionary
scenario for the least massive, most gas-poor objects. The most consistent
characteristic of our sample is that the ratio, R, of HII linewidth to HI 21 cm
linewidth (W_20) are systematically less than unity. The simplest explanation
is that the ionized gas is more centrally concentrated than the neutral gas
within the gravitational potential. On average R=0.66 +/- 0.16, similar to
findings for local HII galaxies. We find R is also a function of linewidth;
smaller linewidth galaxies have smaller values of R. Correcting optical
linewidths by this factor raises derived masses and places these galaxies on
the local luminosity--linewidth (Tully-Fisher) relation. If this ratio applies
to intermediate-redshift galaxies, then the proposed luminosity evolution of
the Tully-Fisher relation is much smaller and more gradual than suggested by
studies using optical emission-linewidth measurements.
