  We study the low-temperature electron mobility of InSb nanowires. We extract
the mobility at 4.2 Kelvin by means of field effect transport measurements
using a model consisting of a nanowire-transistor with contact resistances.
This model enables an accurate extraction of device parameters, thereby
allowing for a systematic study of the nanowire mobility. We identify factors
affecting the mobility, and after optimization obtain a field effect mobility
of $\sim2.5\mathbin{\times}10^4$ cm$^2$/Vs. We further demonstrate the
reproducibility of these mobility values which are among the highest reported
for nanowires. Our investigations indicate that the mobility is currently
limited by adsorption of molecules to the nanowire surface and/or the
substrate.
