  A new nine-dimensional potential energy surface (PES) for methane has been
generated using state-of-the-art \textit{ab initio} theory. The PES is based on
explicitly correlated coupled cluster calculations with extrapolation to the
complete basis set limit and incorporates a range of higher-level additive
energy corrections. These include: core-valence electron correlation,
higher-order coupled cluster terms beyond perturbative triples, scalar
relativistic effects and the diagonal Born-Oppenheimer correction.
Sub-wavenumber accuracy is achieved for the majority of experimentally known
vibrational energy levels with the four fundamentals of $^{12}$CH$_4$
reproduced with a root-mean-square error of $0.70{\,}$cm$^{-1}$. The computed
\textit{ab initio} equilibrium C{--}H bond length is in excellent agreement
with previous values despite pure rotational energies displaying minor
systematic errors as $J$ (rotational excitation) increases. It is shown that
these errors can be significantly reduced by adjusting the equilibrium
geometry. The PES represents the most accurate \textit{ab initio} surface to
date and will serve as a good starting point for empirical refinement.
