OnePay, a consumer financial technology company with ties to Walmart, is giving users at least $1 per gallon back on gas purchased on Wednesdays through Sept. 15, ideal for those filling up before, during and after those long summer vacation road trips.

AAA put the national average for a gallon of regular gas at just over $4 on Aug. 5, so with this $1 back per gallon offer, you could get roughly a quarter off the average pump price before factoring in additional savings through a fuel rewards program or one of the best gas credit cards.

To take advantage of this deal, here’s everything you need to know.

Related: Get up to 5% cash back on Walmart purchases with the new OnePay CashRewards Card

How the OnePay Wednesday deal works

OnePay runs rotating gas offers inside its app (one of which you must activate before you fill up), and each one carries its own cash-back rate. The Wednesday promotion adds $1 per gallon on top of whatever that offer already pays and any cash back you earn from selecting gas as your monthly cash-back category, so you have the potential to save more than $1 per gallon.

Rewards are posted as OnePay Points that you can redeem as a deposit into a OnePay account and use for future gas purchases or anything else you pay by card.

The bonus only applies to purchases made on a Wednesday, which OnePay defines as midnight to 11:59 p.m. PDT. Drivers on the East Coast should pay close attention to the time when planning their fill-ups, as the qualifying window spans a couple of days for them (opening at 3 a.m. EDT on Wednesdays and closing at 2:59 a.m. on Thursdays).

Because the promotion ends Sept. 15, which falls on a Tuesday, only five qualifying Wednesday dates remain for this promotion: Aug. 12, Aug. 19, Aug. 26, Sept. 2 and Sept. 9.

Related: 7 tips to get the most out of a tank of gas

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What you need to do to save at least $1 per gallon on gas this summer

To save on gas through this OnePay deal, you’ll need to take the following steps:

1. Download and open the OnePay app, and go to the Rewards section.
2. Activate a gas offer at a participating station near you.
3. Fill up on one of the remaining qualifying Wednesday dates.
4. Pay with an eligible OnePay payment method.

If you are paying with the OnePay CashRewards Card (see rates and fees) or a third-party card linked to your OnePay Wallet, OnePay requires you to tap or swipe the physical card (not a virtual one), so don’t forget this before you leave the house. OnePay debit cards and OnePay builder cards can earn either way.

Three key restrictions apply:

• Gas offers are not available in New Jersey or Wisconsin.
• Cash-back caps vary by offer. OnePay’s terms tie the $1 off to the limits of whichever gas offer you activate, and those limits can be spending caps or gallon caps that differ from one station to the next. Check the individual offer in the app before you start pumping to ensure you will get at least $1 back per gallon on a full tank of gas.
• OnePay reserves the right to modify or cancel the bonus at any time, with or without notice.

Related: How to use GasBuddy to beat rising fuel prices

Bottom line

A dollar per gallon back is a generous return on a purchase you were making anyway, and the fact that it stacks with OnePay’s standard gas offers makes it even better. If you live near a participating station (there are over 18,000 nationwide), it’s worth checking the app before your next fill-up.

Take the time now to download the app and activate the offer. Then, try and time your regular fill-ups to fall on Wednesdays between now and Sept. 9 for maximum savings.

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