For Rex Tillerson fracking is more than a revolutionary approach to drilling oil and gas — it’s part of his personal history. Simply mention the word to the CEO of Exxon Mobil and he starts reminiscing about his days as a young engineer. It was 1976, and Tillerson had been sent to East Texas for his second assignment at the company. His job was to follow around rigs drilling for natural gas and “complete” the wells. That meant experimenting with a process known as hydraulic fracturing, or fracking. By pumping water, sand, and chemicals down into a well at high pressure, he could cause cracks in the stone where the gas was trapped and allow more of it to flow.