  The list of interesting electrical properties exhibited by transition metal
dichalcogenides has grown with the discovery of extremely large
magnetoresistance (MR) and type-II Weyl semimetal behaviour in WTe$_2$ and
MoTe$_2$. The extremely large MR in WTe$_2$ is still not adequately understood.
Here, we systematically study the effect of Mo substitution on the quantum
oscillations in the MR in WTe$_2$. The MR decreases with Mo substitution,
however, the carrier concentrations extracted from the quantum oscillations
show that the charge compensation improves. We believe that earlier
interpretations based on the two-band theory, which attribute the decrease in
MR to charge imbalance, could be incorrect due to over-parametrization. We
attribute the decrease in MR in the presence of charge compensation to a fall
in transport mobility, which is evident from the residual resistivity ratio
data. The quantum scattering time and the effective masses do not change within
experimental errors upon substitution.
