The spreadsheet tries to tease apart the two competing forces, and finds that -- all else being equal -- each 10 percent rise in gas prices is, in fact, accompanied by a 1 percent decline in gasoline sales within a year. Which suggests that had gas prices remained stable over the past few years, consumption would have risen even faster than it did.

It should come as little surprise that over short time horizons substantial gas-price hikes only reduce sales a small amount. People have only so much flexibility to reduce their gas consumption over the short term -- a fact that economists have understood for years.

But what remains to be seen is whether a sustained increase in gas prices will be accompanied by deeper declines in sales, as people begin to change houses, jobs, or cars to account for higher transportation costs. That's what economists predict will happen; but we'll just have to wait to see how well reality matches up with theory.