Gas prices are higher than they were last year and are expected to rise in the next few months, but there’s one way drivers can still save when fueling up: knowing which day of the week is cheapest to buy gas.

GasBuddy, an app that lets you search for the cheapest gas in your area, published a study finding that so far in 2017, Monday has been the best day of the week to buy gas (in 23 states).

GasBuddy analyzed three years worth of fuel price data and found that the beginning of the week – Monday in particular – offers the lowest average over that period, while Thursday has the most expensive average.

What’s behind the increase in prices toward the end of the week? It might be the weekly report from the Energy Information Administration. The report, released every Wednesday, could push prices higher the day after said Patrick DeHaan, senior petroleum analyst at GasBuddy. “The EIA report, if surprising, can drive markets significantly in either direction. Sometimes that can be both up or down, but an upward move tends to be passed on more quickly than price drops,” DeHaan said.

“Since commodities trading isn’t active over the weekend, it typically allows stations to ‘let it ride’ over the weekend, culminating in lower prices by the start of the work week,” he said.

GasBuddy estimates that if every American driver fueled up on Thursday for an entire year, they’d spend an extra $1.1 billion compared with buying gas on Monday.

The study found that the best day to buy gas depends on what part of the country you’re in. Findings include:

?In 2017 so far, Monday is the best day of the week in 23 states.

?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.

The national average is currently $2.40 a gallon, according to AAA – up from $2.17 a year ago. AAA predicts prices will continue to rise into the summer.

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