The research on coexistence between marine gas hydrates and deepwater petroleum systems has great significance to exploration and exploitation of both deepwater hydrocarbon reservoirs and shallow gas hydrates, to the inducement of submarine slide and to the development of new insights on global climate change and earth’s carbon cycle. The new advances in leaking, capping and capping side-accumulation coexistence relationship are systematically summarized. According to the investigation, for the most part, the contributions of deep-seated oil and gas to shallow gas hydrate field have likely been underappreciated. The restricted discrimination among different sources of carbon trapped within gas hydrate confines the recognition of leaking coexistence between deepwater petroleum systems and shallow gas hydrates. Significant attention has been paid to the hydrocarbon supply from deflected hydrocarbon migration by low-permeability hydrate-bearing sediments and gas hydrates dissociation during geological history to conventional petroleum accumulations. Except for very few geological provinces, the resource potential of free gas trapped beneath gas hydrate is not significant. In most cases, gas hydrate-bearing sediments are not a high quality seal, unless structural, stratigraphic, lithologic, or/and permafrost traps have been involved, forming a relatively effective trap for upward hydrocarbon flow. We suggest as additional research on how to assess hydrate-bound gas sources from sub-biogenetic gas and secondary biogenic gas produced by anaerobic biodegradation of crude oil and thermogenic gas, and to illuminate the low trapping capacity of gas hydrate-bearing sediments by mathematic model.