There’s a rule of thumb that says a $10 rise in the price of a barrel of oil reduces gross domestic product growth by anywhere from 0.2 to 0.5 percentage points. Applied over the past six months, when crude prices rose by about $30 from early October to the end of March, that means dearer oil might’ve chewed as much as 1.5 percent out of GDP growth during the last two quarters. Not a trivial amount considering GDP increased 3 percent in the fourth quarter of 2011. Economists surveyed by Bloomberg tend to think the economy grew just 2.2 percent in the first three months of 2012, when the price of gas really took off.