An alternative to time sequence evaluation of field size distributions is presented. Oil fields are ranked in relation to level of prior exploration in the vicinity of discovery wells. Field size distribution patterns for discoveries at sequential levels of prior exploration are evaluated independently from the time sequence of discoveries within the region. Interregional comparisons are made in terms of field discoveries at equivalent levels of prior exploration. The study area covers a large region (approximately 78,000 Km2) of central and northwest Kansas. ?? 1985 Plenum Publishing Corporation.