Hubbert was invited to give the spring meeting of the Southwest Section of the American Petroleum Institute a broad brush picture of the overall world energy situation on March 8, 1956. As he listened to the Mayor of San Antonio's welcome address, ready to give his speech, Hubbert received a signal to leave the platform. In a desperate last-minute phone call, a public relations representative of his employer Shell Oil implored Hubbert to “tone down” the “sensational parts” of his speech.
Hubbert declined and went on to give his seminal speech. He explained to the audience the stages of growth of extraction along a bell curve and how the point of inversion from concave to convex can be used to predict when the rate of growth would stop and therefore the extraction would peak before the rate of growth went negative. Knowing that the production started at zero and ended at zero simplified the mathematics such that he was able forecast the peaking of the lower 48 states given an estimate of total recoverable reserves. Rather than conjure up his own numbers, Hubbert used the range of the estimates from the most highly regarded geologists at the time – 150 to 200 million barrels. Simply graphing the curves and counting squares, he showed that lower 48 states would peak between 1965 and 1971.
He also plotted oil on a scale of 10,000 years - 5,000 years ago to 5,000 years in the future – showing Man’s use of petroleum is “a unique event in human history, a unique event in biological history. It is non-repetitive, a blip in the span of time.”
Hubbert’s forecast caused shock, consternation, and denial in various parts of the petroleum industry. He would later say “that caused a jolt instead of palming off the shortage on our grandchildren, we found ourselves staring it right in the face. The first reaction was honest incredulity. Then the industry split. One side refused to accept the situation and starting changing the figures. The other side, people like Shell, found they could not change the figures.”