CHICAGO (CBS) — When is the best time to fill up your car with gasoline?

Besides “before it’s empty.”

According to an analysis by Gas Buddy, the best day of the week in Illinois in 2013 to fill up was Saturday.

It hasn’t always been that way.

In 2010: Sunday

In 2011: Monday

In 2012: Friday

In Indiana, it’s been consistent for the past four years.

Fill’er up on Monday!

In Wisconsin, it was Saturday in 2013.

The average price for a gallon of gasoline in Chicago this week is $3.53.

As always, it’s cheaper in Indiana, at $3.20.

“Surprisingly, many states see the lowest gasoline prices for the week during the weekend, which may come as a surprise to many motorists,” said Patrick DeHaan, senior petroleum analyst with

According to the analysis, 65 percent of states saw lower prices during the weekend than the week, which included Friday, Saturday, or Sunday.

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