The issue:

Americans depend on energy for everything from driving their cars to powering factories, homes and offices — and of course our smartphones, laptops and tablets. How that energy is produced and where it comes from affect jobs, the economy and the environment.

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Where they stand:

President Barack Obama proposes an "all of the above" strategy that embraces traditional energy sources such as oil and coal, along with natural gas, nuclear power and renewable sources such as wind, solar and hydropower. Obama has spent billions to promote "green energy" and backs a tax credit for the wind industry that his Republican rival Mitt Romney opposes. While production of renewable energy has soared, critics point to several high-profile failures, including Solyndra, a California solar company that went bankrupt, costing taxpayers more than $500 million.

Romney pledges to make the U.S. independent of energy sources outside of North America by 2020, through more aggressive exploitation of domestic oil, gas, coal and other resources and quick approval of the Keystone XL pipeline from Canada to Texas. Obama blocked the pipeline because of environmental concerns but supports approval of a segment of it.

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Why it matters:

Every president since Richard Nixon has promised energy independence — a goal that remains elusive. In 2011, the U.S. relied on net imports for about 45 percent of the petroleum it used, much from Canada, Mexico and Saudi Arabia. Still, U.S. dependence on imported oil has declined in recent years, in part because of the economic downturn, improved efficiency and changes in consumer behavior. At the same time, domestic production of all types of energy has increased, spurred by improved drilling techniques and discoveries of vast oil supplies in North Dakota and natural gas in states such as Pennsylvania, Ohio, New York and West Virginia. Production also is booming in traditional energy states such as Texas, Oklahoma and Louisiana.

The natural gas boom has led to increased production, jobs and profits — and a drop in natural gas prices for consumers. Natural gas, a cleaner alternative to coal, has generally been embraced by politicians from both parties.

Still, there are concerns. Critics worry that popular drilling techniques, such as hydraulic fracturing and horizontal drilling, which allow drillers to reach previously inaccessible wells, could harm air, water and health. Hydraulic fracturing, also called fracking, involves blasting mixtures of water, sand and chemicals deep underground to stimulate the release of gas. Environmental groups and some public health advocates say the chemicals have polluted drinking water supplies, but the industry says there is no proof.

Similarly, the Keystone XL pipeline could help make the nation more energy secure — or pollute the environment in the event of a spill. Developer TransCanada says the 1,700-mile pipeline from western Canada to refineries along the Texas Gulf Coast would pipe more than 1 million barrels of oil per day, more than 5 percent of the nation's current oil consumption.

Opponents say the pipeline would bring "dirty oil" that would be hard to clean up after a spill.

Wind and solar power have grown, thanks in part to support from Obama, but their success is tenuous. Besides Solyndra, several solar companies have declared bankruptcy in part because of Chinese competition. Wind companies are laying off workers while Congress dithers on a tax credit crucial to the industry.

The changes aren't likely to have an immediate effect on the cost of the energy source Americans are most familiar with: gasoline. Gas prices are dependent on crude oil prices, which are set on the global market.

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Follow Matthew Daly on Twitter: https://twitter.com/MatthewDalyWDC

EDITOR'S NOTE _ One in a series examining issues at stake in the election and their impact on people