Because petrochemicals are key components to much more than just the gas in your car. Approximately 10 calories of fossil fuels are required to produce every 1 calorie of food eaten in the US. The size of this ratio stems from the fact that every step of modern food production is fossil fuel and petrochemical powered:

Pesticides and agro-chemicals are made from oil; Commercial fertilizers are made from ammonia, which is made from natural gas. Most farming implements such as tractors and trailers are constructed and powered using oil-derived fuels. Food storage systems such as refrigerators are manufactured in oil-powered plants, distributed using oil-powered transportation networks and usually run on electricity, which most often comes from natural gas or coal. In the US, the average piece of food is transported almost 1,500 miles before it gets to your plate.

It's not just transportation and agriculture that are entirely dependent on oil. Modern medicine, water distribution, and national defense are each entirely powered by oil and petroleum derived chemicals. In addition to transportation, food, water, and modern medicine, mass quantities of oil are required for all plastics, all computers and all high-tech devices.

Automobiles

The construction of an average car consumes the energy equivalent of approximately 20 barrels (840 gallons) of oil. Ultimately, the construction of a car will consume an amount of fossil fuels equivalent to twice the car’s final weight.

Computers

The construction of the average desktop computer consumes ten times its weight in fossil fuels.

Microchips

The production of one gram of microchips consumes 630 grams of fossil fuels. According to the American Chemical Society, the construction of single 32 megabyte DRAM chip requires 3.5 pounds of fossil fuels. The Environmental Literacy Council tells us that due to the "purity and sophistication of materials (needed for) a microchip, . . . the energy used in producing nine or ten computers is enough to produce an automobile."

Concrete and Highways

The manufacturing of one ton of cement requires 4.7 million BTUs of energy, which is the amount contained in about 45 gallons of oil.

Alternative Energy

When considering the role of oil in the production of modern technology, remember that most alternative systems of energy — including solar panels/solar-nanotechnology, windmills, hydrogen fuel cells, biodiesel production facilities, nuclear power plants, etc. all rely on sophisticated technology and energy-intensive forms of fossil fuels. In fact, all electrical devices make use of silver, copper, aluminum and platinum, each of which is discovered, extracted, and fashioned using oil or natural gas powered machinery. Nuclear energy requires uranium, which is also discovered, extracted, and transported using oil powered machinery.