  Large unsaturated magnetoresistance has been recently reported in numerous
semi-metals. Many of them have a topologically non-trivial band dispersion,
such as Weyl nodes or lines. Here, we show that elemental antimony displays the
largest high-field magnetoresistance among all known semi-metals. We present a
detailed study of the angle-dependent magnetoresistance and use a
semi-classical framework invoking an anisotropic mobility tensor to fit the
data. A slight deviation from perfect compensation and a modest variation with
magnetic field of the components of the mobility tensor are required to attain
perfect fits at arbitrary strength and orientation of magnetic field in the
entire temperature window of study. Our results demonstrate that large orbital
magnetoresistance is an unavoidable consequence of low carrier concentration
and the sub-quadratic magnetoresistance seen in many semi-metals can be
attributed to field-dependent mobility, expected whenever the disorder
length-scale exceeds the Fermi wavelength.
