Appraisal of prospects in advance of drilling almost invariably involves predicting the amount of oil that may be discovered using only indirect evidence such as seismic maps and profiles. A widely used appraisal method, the Monte Carlo technique, requires geologic information that cannot be known prior to drilling, necessitating the use of estimates that may be highly uncertain. The results of Monte Carlo analysis may be misleading if the assumed geologic parameters are not accurate. Simple statistical procedures based on regressions between seismic characteristics that are discernible before drilling and the volumes of oil and gas subsequently discovered in prospects provide an alternative objective basis for prospect appraisal. To demonstrate the method, structural prospects were evaluated in part of the Pleistocene trend of offshore Louisiana and Texas. Highly significant statistical relationships were found between structural properties measured on prospects shown on regional seismic reconnaissance maps, including area of structural closure, and the volumes of oil and gas subsequently discovered by drilling these prospects. Statistical procedures based on seismic information may be more than twice as effective as Monte Carlo methods.--Modified journal abstract.