For most of human history, the dominant concerns about energy have centered on the benefit side. Inadequacy of energy resources of the technologies for harvesting, converting, and distributing those resources has meant insufficient energy benefits to human beings and hence inconvenience, and constraints on its growth. The 1970's, then, represented a turning point. Energy was seen to be getting costlier in all respects. It began to be believable that excessive energy costs could pose threats on a par with those of insufficient supply. It also became possible to think that expanding some forms of energy supply could create costs exceeding the benefits. The crucial question at the beginning of the 1990's is whether the trend that began in the 1970's will prove to be temporary or permanent. Is the era of cheap energy really over, or will a combination of new resources, new technology and changing geopolitics bring it back? One key determinant of the answer is the staggering scale of energy demand brought forth by 100 years of population growth and industrial demand. Except for the huge pool of oil underlying the Middle East, the cheapest oil and gas are already gone. Even if a few more giant oil fields are discovered, they will make little difference against consumption on today's scale. Oil and gas will have to come increasingly, for most countries, from deeper in the earth and from imports whose reliability and afford-ability cannot be guaranteed.