Later, when the flow has slowed down, water is sometimes injected below the oil pocket, or gas above the oil pocket, to keep production going. These combined primary and secondary recovery measures can extract about one-third of a typical deposit. Tertiary or enhanced recovery is expensive and involves pumping steam into the well to heat and thin heavy oil and get it to flow into the well bore.

Although the internal combustion engine was invented shortly after the birth of the oil industry, it was many years before car engines became a significant consumer of oil products. Initially, oil was used in medicine, as a lubricant, and to light lamps. Now, with more than 26.8 million motor vehicles in Texas alone (2007), oil is being consumed at a rapid pace. The United States consumes 20 million barrels of oil products each day, or 23 percent of the world's daily production (2008).

Figure 6 Sources of U.S. petroleum, 2008 Source: U.S. Department of Energy