If you're like me, and I know I am--you've never really considered what day of the week it is while stopping to fill up with gas. I mean, call me old school, but I generally fill up when it appears that my tank is low and in need of a refuel. Now I find out that's been costing me money.

The website GasBuddy.com makes it their business to know (and share) all things gasoline. They cover a variety of petrol-related topics, like gas price maps, trip calculators, gas price charts, fuel insights, etc. Yesterday, GasBuddy revealed "The Best Day of the Week to Buy Gas."

GasBuddy analyzed three years worth of fuel price data and found that Monday offers the lowest average, making it the best day to fill up. Thursday is the worst day to buy gas, having the most expensive average. However, the best day depends on what part of the country drivers are located:

In 2017 so far, Monday is the best day of the week in 23 states (including Illinois)
In 2016, Monday was the day featuring the lowest average gasoline prices in 36 states, while eight states saw Tuesday as the victor.
In 2015, Monday saw the lowest gasoline prices in 22 states.
In 2014, Wednesday was the day of the week offering the lowest average gasoline prices.

So, in the big picture, how much difference could it make buying gas on a Thursday or Friday rather than Monday?

To put the amount of savings into perspective: if every U.S. motorist bought gasoline on Thursday for an entire year, they’d collectively spend an extra $1.1 billion versus filling up on Monday – the lowest priced day of the week.

Of course, in some of these places, it really doesn't matter what day you pull up to the pump:

See you in the Monday line at the pump!