  At low redshift, the majority of supermassive black hole (SMBH) mass
estimates are obtained from modeling stellar kinematics or ionized gas dynamics
in the vicinity of the galaxy nucleus. For large early type galaxies, stellar
kinematics models predict higher masses than gas-dynamical models. In the case
of M87, this discrepancy is larger than 2 $\sigma$. Critical to gas-dynamical
modeling is the assumed underlying dynamical state of the gas: that it lies on
circular Keplerian orbits, potentially with some additional turbulent pressure
support. This is inconsistent with models of the gas flow about
low-accretion-rate SMBHs and at odds with observations of the Galactic Center.
We present a simple model for non-Keplerian gas disks and explore their
implications for SMBH mass measurements. We show that a larger central black
hole with gas experiencing small amounts of sub-Keplerian motion can produce
velocity curves similar to models that just contain circular Keplerian motions
and a lower black hole mass. However, these non-Keplerian models are
distinguishable from low-mass Keplerian models primarily through measurements
of the velocity dispersion, wherein non-Keplerian models produce higher and
narrower peak dispersions. Away from the galaxy center, but still within the
circumnuclear gas disk, non-Keplerian models also become distinguishable from
Keplerian models via a shift in the velocity curve. The velocity model
presented in this paper is capable of resolving the discrepancy between the
ionized gas dynamics and stellar kinematics mass estimates, and is applicable
to gas-dynamical mass estimates of SMBHs in general.
