Consumption is the key. With small fluctuations, U.S. oil usage has climbed steadily for the past 50 years. From 5.6 Mb/d in 1949 (6% supplied by imports) to 13.8 Mb/d in 1970 (23% from imports) and 20 Mb/d in 2004 (60% from imports), America's unrelenting thirst for petroleum has driven the consumer end of the market for a hundred years. And by late 2005, consumption had climbed to 20.5 Mb/d, fueled by net imports of 13.2 Mb/d - more than 64% of the total.

How much is 20 million barrels a day? A 42-gallon oil barrel is maybe four feet high. If you laid 20 million of them end to end, they would stretch more than 15,000 miles - every day! In terms of gallons of all oil products, if a 1-gallon can is a foot wide, lined up those cans would extend about 163,000 miles - enough to circle the earth at the equator 6½ times - every day.

Not all the oil used goes to make gasoline, of course - there's fuel oil, jet fuel, the chemicals to make all the plastic in the world, as well as lubricants, greases, lipstick and petroleum jelly. But U.S. consumption of gasoline is astonishing - we burn it up at a rate averaging more than 320 million gallons per day, or about 3700 gallons per second, 24 hours a day, 7 days a week. That's enough one-foot-square gallon cans to cover a football field every nine seconds.

So which countries supply our imported oil? Few people can name the top four countries, which together supply about 60% of our crude oil imports. In August 2005, Canada and Mexico were in a virtual tie for first, each providing about 16% of total imported petroleum. Saudi Arabia, which most people would include on the top four list, was No. 3 with about 14%. Venezuela (13%) rounds out the top four sources of American oil. Up-and-coming Nigeria is Number 5, with 11% of our imports. The rest of the top 10, in order, are Angola with 6% and Iraq, Algeria, United Kingdom, and Ecuador, at about 3% of our imports each.

The amount of oil we import from each country fluctuates somewhat from month to month and year to year. For most of the past 5 years, Canada was the clear leader, at about 17-18%, and Saudi Arabia was number 2, with 14-15%. During the 1960s, Venezuela was far and away our greatest supplier.

What can be done about our import dependency? Drill more wells? In 1972 we had 508,000 pumping wells. Many of those wells have dried up or become uneconomical to operate, but despite that, in 2004 about 510,000 wells were pumping oil. We're drilling about as many new wells as we can, both technologically and economically. The problem is the average volume per well - down from almost 19 barrels per well per day in 1972 to about 10.5 barrels per well per day in 2004. The same number of wells pumps only about half the oil of 30 years ago. You can't make a 10-barrel-a-day well pump 1,000 barrels, no matter what you do. There are some enhancement techniques that squeeze the last drops out of an oil field, but those are short-term fixes that do not provide great volumes of crude.

In contrast to America's 10-barrel-per-day average for each well, the few wells in Saudi Arabia average about 6,500 barrels per day per well.

What about ANWR - the Arctic National Wildlife Refuge? The controversy rages. As of today, there is no known oil in ANWR - it can't be known until the rocks are drilled. The U.S. Geological Survey, using sophisticated estimation techniques that factor in the geology and other "knowns," gives a best guess for the amount of oil that MAY be in ANWR at 10.4 billion barrels of technically recoverable oil. That sounds like a lot, but it's less than Prudhoe Bay contained. At about 13 billion barrels, Prudhoe was the largest oil field in North America, but most of its oil has been produced. In contrast, the world's largest oil field, Ghawar in Saudi Arabia, contained about 85 billion barrels, with much remaining.

That guesstimate of 10.4 billion barrels in ANWR works out to 520 days' supply at our current rate of consumption. But in reality, even if it's there, it won't be produced in a whoosh. Any oil will take years to come on-stream, and will be produced over a period of perhaps 20 years. A reasonable production rate over that time would be one million barrels per day - just 5% of today's 20 Mb/d consumption. Given that our rate of consumption is increasing by 4% to 5% each year, all the possible oil in ANWR would do nothing but help keep pace with demand growth. Helpful, but no panacea.

The deep-water Gulf of Mexico offers some possibilities for major oil finds. Such exploration and production is expensive, and once established runs the risk of shut-downs because of hurricane damage, as we know well after the season of 2005. Offshore California has potential, but stringent environmental regulations have reduced exploration there to virtually zero.

Can Montana help? Montana IS helping. Because many of their fields are small, old and largely tapped out, traditional oil-patch states are losing oil production at increasing rates. Texas' production fell by almost 7% between 2004 and 2005 while Louisiana lost not quite 2%; California declined by 2%, and New Mexico lost almost 5% of its production rate. At the same time, Montana, ranking #10 on the list of oil producing states, increased its production by more than 14%, to 88,000 barrels per day in June 2005. That volume is paltry compared to leaders like Louisiana, averaging 1,463,000 barrels per day in 2005, but the Montana rate of increase is dramatic. Compared to 2002, Montana's oil production has grown by a whopping 87%.

The growth in Montana production is also enjoyed by North Dakota, which shares the oil-rich Williston Basin with eastern Montana. A package of rock called the Bakken Formation, laid down around 360 million years ago, is the key to the new production. Averaging just 8 to 12 feet thick, the pay zone is exploited by a relatively new technique called horizontal drilling, which punches the drill along the length of a rock layer rather than straight through it. This exposes much more of the oil-bearing rock to the drill hole, allowing more oil to be extracted. Best estimates by many economists see no end in sight for this increase, and some optimistic folks suggest that Montana could be producing as much as 200,000 barrels per day within 5 years, jumping it to the Number 5 ranking among the states, after Louisiana, Texas, Alaska, and California. It could happen, but without major changes in consumption habits, oil price shocks are likely to be the rule rather than the exception.

Sources: Most statistics in this article are from the U.S. Energy Information Administration.