MINNEAPOLIS (WCCO) – In the span of a week, we’ve seen gas prices spike across the Twin Cities.

AAA says a gallon of unleaded was going for $3.56 last week. That number jumped more than 20 cents to $3.77 yesterday.

And online price trackers say many gas stations are now selling it for as much as $3.89.

“It’s a tough time to be driving, but a lot of people are,” said Gail Weinholzer of AAA.

Weinholzer said there are four major reasons for the sudden increase.

One: Crude oil prices have risen almost $15 a barrel since the Fourth of July.

Two: Drought is having an impact on corn crops, which is causing ethanol prices to go up.

Three: This is a busy travel time before kids go back to school.

And four: The Enbridge Pipeline in Wisconsin began leaking about 10 days ago, causing fuel to be diverted from other areas.

“We’ve seen it happen before in larger numbers, but it wasn’t totally expected at this point,” Weinholzer said. “Of course, it’s hard to predict a drought or a pipeline leakage.”

But she doesn’t believe we will see $4-a-gallon gas anytime soon. That’s because she said the pipeline should be up running again and the summer driving season is almost over.

This fall, we will switch from summer to winter grade fuel, which is less expensive for your car. Prices will drop again, keeping your pocketbook on a roller coaster.

“Just one day being one price and another day being another price — it’s kind of challenging,” said driver, Greer Bingham.

The increase in ethanol is a major part of the increase in gas prices.

That’s because 90-95 percent of all vehicles have at least 10 percent ethanol in their fuel.

To see the lowest gas prices in your area, click here.