WASHINGTON — Why are gasoline prices so high? Why have they shot up so fast? Why don't they fall back as quickly when the price of oil dips?

Here are some answers.

Q. Why are gas prices so high?

A. Global demand for oil has grown quickly in recent years, driven up especially by China's and India's fast-growing economies, although the United States by far remains the biggest oil consumer. Global demand for oil is about 84 million barrels per day. That almost equals the entire supply available; oil-production capacity exceeds demand by only about 1.5 million to 2 million barrels per day.

In such circumstances, anyone who needs oil soon must pay what the market asks, since there aren't many sellers with excess oil available. In addition, with the supply-demand balance so tight, markets fear that a single terrorist act, a natural disaster such as a hurricane or earthquake, or even an accident at a major refinery could spark shortages. So buyers are willing to pay higher prices today to ensure that they will get what they need tomorrow if supplies are short.

Q. Why did oil prices rise so fast?

A. The price of crude oil jumped dramatically in part because of heightened fears of shortages. Oil traders are particularly nervous about forecasts of a busier-than-usual hurricane season. Hurricanes disrupt deliveries by oil tankers and can halt production at offshore rigs in the Gulf of Mexico. They also threaten refineries on the Gulf Coast. Other factors included temporary shutdowns at some U.S. refineries and U.S. government warnings of possible terrorist attacks in Saudi Arabia, the world's biggest oil producer.

Q. Prices in my neighborhood are higher than a few blocks away. Is this price gouging?

A. No. Gas stations can charge what the market will bear. Gas prices are set through "zone pricing." Wholesalers of gasoline have complex software programs that gauge the income and population density of neighborhoods. They set higher prices for retailers in areas with higher income and population density.

Q. After rising this month to more than $67 per barrel, oil prices are in the $65 range. Why didn't gas prices drop, too?

A. Rockets and feathers. It's an industry expression to say prices rocket up but drop as slowly as a feather. Economists have documented this. One dealer said privately that it simply was profit taking to make up for losses when consumers bought less gas because of higher prices.

Q. Aren't oil cartels to blame for the high prices?

A. Prices today are driven by demand, not supplier-imposed shortages as in the 1970s and '80s. The Organization of Petroleum Exporting Countries says its members are pumping oil at almost full throttle and that developed nations should build more refineries.

Q. So refiners are to blame?

A. Critics allege that refiners avoided adding capacity in order to create a tight market that gives them greater profits. The industry says environmental regulations and local opposition make it impossible to site new refineries. Financial experts say low return on investment is the real reason that refineries, which cost billions of dollars, haven't been built for years.

Q. Is this the peak?

A. Analysts have said prices may exceed $70 a barrel, and a shock event could drive them toward $100.

Q. Will prices ever fall significantly?

A. Award-winning oil historian Daniel Yergin predicts global production capacity will expand by 2010 to yield an additional 16 million barrels of oil per day. He suggests an oil glut that causes a collapse in prices.

Matthew Simmons, an investment banker who specializes in oil, wrote a controversial new book, "Twilight in the Desert," suggesting Saudi production has peaked and soon will shrink. To Simmons, $3 a gallon sounds cheap compared with what's coming.