近四十年来,美国新发现的油气田的规模出现了一种持续下降的趋势。譬如,1945～1950年新发现的单个油气田的储量平均为140万吨石油当量,而八十年代初降到了25万吨石油当量。出现这种趋势的一个重要原因是,发现天然气田的比例增加了:如果说五 In the past 40 years, the scale of newly discovered oil and gas fields in the United States has experienced a continuous decline. For example, the newly discovered single oil and gas field from 1945 to 1950 had an average of 1.4 million tons of oil equivalent, which fell to 250,000 tons of oil equivalent in the early 1980s. An important reason for this trend is that the proportion of natural gas fields discovered has increased: if five