  We consider the Standard Model extended by the addition of a complex scalar
singlet, with no assumptions about additional symmetries of the potential. This
model provides for resonant di-Higgs production of Higgs particles with
different masses. We demonstrate that regions of parameter space allowed by
precision electroweak measurements, experimental limits on single Higgs
production, and perturbative unitarity allow for large di-Higgs production
rates relative to the SM rates. In this scenario, the dominant production
mechanism of the new scalar states is di-Higgs production. Results are
presented for $\sqrt{S}=13$, $27$ and $100~TeV$.
