How high could U.S. gas prices rise in the decade ahead? That's one of the toughest price levels to forecast, due to the number and unpredictability of the variables that affect gas prices.

The average U.S. price of regular unleaded gas was $3.62 per gallon, based on data collected by  That's up a horrible 91 cents or about 33 percent from a year ago, in July 2010.

Here are two gas price scenarios through the end of 2012:

Moderate GDP Growth Scenario: This scenario assumes that the U.S. economic recovery will continue at a moderate pace, that Europe's economy (in euro-zone nations) will grow at a sluggish pace, and that China's white-hot emerging market economy (which strong demand for oil) will continue to grow at least 7-8% per year in both 2011 and 2012.

This scenario also assumes that Libya's civil war will end with the ouster of Leader Muammar Qaddafi and at least a portion, or about 500,000 barrels per day (bpd)  of the country's 1.7 million bpd production (and 1 million bpd export production) will resume. Due to civil war damage and related threats, Libya is currently producing just 100,000 bpd.

Assuming the above, a plausible case can be made for oil prices remaining in the $80-$110 per barrel range through the end of 2012, and that would keep the average U.S. gasoline price for regular unleaded at about $3.40-3.80 per gallon.

Strong GDP Growth Scenario: This scenario assumes that better quarters are ahead for the U.S. economy, i.e. that GDP growth quickens, to a 3.5-4% rate, and that job growth of at least 150,000 new jobs per month returns by the fall 2011. This scenario also assumes moderate GDP growth in Europe, a strong economy in China, and a favorable outcome to the Libyan civil war (cited above).

Under this stronger U.S. economy scenario, oil prices remain above $100 per barrel and push toward $120 per barrel by the end of 2012.

If oil trades in a $100-120 per barrel range, that would mean average U.S. gasoline prices for regular unleaded of about $3.80-4.20 per gallon, with the latter occuring toward the end of 2012.

Oil/Gasoline Analysis: Of course, the two above scenarios don't consider what can not be forecast -- the outbreak of new wars (particularly in the oil-rich Middle East), weather events (such as hurricanes affect U.S Gulf of Mexico oil and refining installations), or oil embargoes by key producers (especially OPEC).

The bottom line for U.S. motorists? Unless there's a wholesale switch to an alternate fuel(s) or a sudden, collapse in global oil demand, look for U.S. gasoline prices to remain well above $3. In other words, it appears the days of $2-something per gallon gasoline are gone.