Natural gas wells contaminated with the toxic gas hydrogen sulfide (i.e., sour-gas wells) pose potential health risks to workers and to nearby residents. The health risks are a function of the dose-response relationship of hydrogen sulfide, the likelihood of accidental releases, gaseous emission rates, the nature of releases at the well head, dispersion of the emitted gas, and the characteristics of the population at risk. We discuss each of these factors and present a risk analysis of a hypothetical sour-gas well in the vicinity of Evanston, WY. We found that the greatest risks for life-threatening effects would occur in the northwest downwind sector after a horizontal release of gas at the well. Subacute effects (e.g., respiratory [...]