By John Dodge

CHICAGO (CBS) — Repairs at BP’s Whiting, Ind., refinery sent gasoline prices plunging last week across Chicago and nationwide, the biggest single-week drop this year.

In Chicago, the average price for a gallon stood at $3.03 on Sunday, which was down 28.7 cents compared with last week, according to GasBuddy.

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One year ago, the average gasoline price was $3.70 a gallon.

The national average is $2.47/gallon–nearly a dollar cheaper than last year.

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“Nationally, gas prices saw their largest weekly drop of the year,” said Patrick DeHaan, GasBuddy senior petroleum analyst.

“Prices moved lower in all but one state, Utah, with plunges at the pump throughout the Great Lakes as a result of BP’s Whiting, Indiana refinery coming back online.

“The national average now stands at its lowest point since April, a fitting way to close out the summer driving season with Labor Day approaching.”

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DeHaan said prices should continue to fall in the next week as the cost at the pump has not fallen in concert with lower oil prices over the summer.