Gas hydrate, which is essentially methane in ice, is a potentially important worldwide energy resource. There is evidence of significant in-place gas hydrate resources in offshore deepwater areas of the world. Southwest Statistical Consulting under grants from U.S Bureau of Ocean Energy Management (BOEM) is developing a mass-balance cell-based model using stochastic simulation to obtain estimates of in-place gas hydrate resources in U.S. Federal off-shore areas. Major components of a gas hydrate petroleum system include a source, in this case organic carbon, appropriate levels of temperature and pressure, and the presence of seals. Approximately 40 submodels are used estimate the potential storage volume, the concentration of the resource, and the charge, and ultimately resource volume. Preliminary in-place results have been published for the Gulf of Mexico where the assessment model structure consists of over 200,000 cells that measure 2.32 km2. Input information is in the form of hard data, analogs, and expert judgment. The challenge is to formulate a model that yield an accurate estimate of undiscovered potential resources and quantify its uncertainty. Both are critical to decision makers. A hierarchical approach is used to address these questions.