『（Abstract）
　Considering the important role played today by unconventional gas resources in North America and their enormous potential for the future around the world, i is vital to both policy makers and industry that the volumes of these resources and the impact of technology on these resources be assessed. To provide for optimal decision making regarding energy policy, research funding, and resource development, it is necessary to reliably quantify the uncertainty in these resource assessments. Since the 1970s, studies to assess potential unconventional gas resources have been conducted by various private and governmental agencies, the most rigorous of which was by the United States Geological Survey (USGS). The USGS employed a cell-based, probabilistic methodology which used analytical equations to calculate distributions of the resources assessed. USGS assessments have generally produced distributions for potential unconventional gas resources that, in our judgment, are unrealistically narrow for what are essentially undiscovered, untested resources. In this article, we present an improved methodology to assess potential unconventional gas resources. Our methodology is a stochastic approach that includes Monte Carlo simulation and correlation between input variables. Application of the improved methodology to the Uinta-Piceance province of Utah and Colorado with USGS data validates the means and standard deviations of resource distributions produced by the USGS methodology, but reveals that these distributions are not right skewed, as expected for a natural resource. Our investigation indicates that the unrealistic shape and width of the gas resource distributions are caused by the use of narrow triangular input parameter distributions. The stochastic methodology proposed here is more versatile and robust than the USGS analytic methodology. Adoption of the methodology, along with a careful examination and revision of input distributions, should allow a more realistic assessment of the uncertainty surrounding potential unconventional gas resources.

Keywords: Resource assessment; unconventional resources; natural gas; uncertainty quantification』

Introduction
Overview of unconventional gas resource assessment in north America
　Existing methodologies
　Description of the USGS methodology
　Potential problems with the USGS methodology
　　Use of mainly triangular distributions
　　Correlation between input variables
　　Concerns with the assumption of perfect correlation in the aggregation from the AU level to the TPS and province level
Improved methodology
Application and results
　Analysis of the Piceance transitional AU
　Analysis of the total Uinta-Piceance province
　　Including correlation between input variables
　　Changing width of input probability distributions
　　Changing shape of input probability distributions
　　Changing width and shape of input probability distributions
　　Including variable correlation with unbounded probability distributions
Conclusions
Acknowledgments
Nomenclature
References