  NGC 2915 is a nearby blue compact dwarf with the HI properties of a late-type
spiral. Its large, rotating HI disk (extending out to R ~ 22 B-band scale
lengths) and apparent lack of stars in the outer HI disk make it a useful
candidate for dark matter studies. New HI synthesis observations of NGC 2915
have been obtained using the Australian Telescope Compact Array. These data are
combined with high-quality 3.6 $\mu$m imaging from the Spitzer Infrared Nearby
Galaxies Survey. The central regions of the HI disk are shown to consist of two
distinct HI concentrations with significantly non-Gaussian line profiles. We
fit a tilted ring model to the HI velocity field to derive a rotation curve.
This is used as input for mass models that determine the contributions from the
stellar and gas disks as well as the dark matter halo. The galaxy is
dark-matter-dominated at nearly all radii. At the last measured point of the
rotation curve, the total mass to blue light ratio is ~ 140 times solar, making
NGC 2915 one of the darkest galaxies known. We show that the stellar disk
cannot account for the steeply-rising portion of the observed rotation curve.
The best-fitting dark matter halo is a pseudo-isothermal sphere with a core
density $\rho_0\sim 0.17 \pm 0.03$ \msun pc$^{-3}$ and a core radius $r_c\sim
0.9 \pm 0.1$ kpc.
