Crude oil futures fell to below $90/barrel Wednesday on the same macroeconomic factors that sunk the grain markets, some of which are poised at multi-month lows.

The lagging oil prices mean gasoline will likely stay below the $4/gallon mark in the Midwest, provided there's no "flare-up" in the parts of the world where much of the U.S. crude oil supply originates, says Purdue University Extension economist Wally Tyner.

"Any disturbance in the Middle East or heightening of tensions with Iran could move crude oil up," Tyner says in a university report. "And that would send gasoline higher."

Though it's good news for drivers, the slowing oil market will likely continue to weigh on the commodity markets, especially if economic growth in places like China continues to slip.

"Economic growth or lack thereof is a major determinant of demand for gasoline. If growth is slower, gasoline prices will be lower. Growth has slowed in China and in Europe," Tyner says. "If that slowdown continues, it would put downward pressure on crude oil and gasoline prices."