It takes 100 points to earn 1 gas reward. Points totaling less than 100 expire at the end of the calendar month in which they were earned. Gas rewards earned during each month can be used through the end of the following calendar month. So you have at most 2 months to use up your gas rewards.
One gas reward gets you $0.10 off per gallon. I don’t think Safeway gas stations have a limit on rewards, but the only ones I’ve ever passed by are in Novato and Vallejo; it looks like there are a couple in Alameda. Unless I’m on those sides of the Bay, crossing bridges kills the deal. Chevron limits gas rewards to 2, or $0.20 off per gallon, per pump. For our 15 gallon tank, that means we save at most $3 per pump. Gas rewards are subject to a limit of 25 gallons anyway, so at most 2 rewards will get you $5 off per pump. We fill up on average two, maybe 3 times a month. And since gas rewards expire in a month or two, it’s very hard to use them all on gas.
The Safeway app gives you other options to use your gas rewards on, including $ off certain grocery items. But Safeway isn’t always the cheapest for certain items, and I find that I can sometimes do better at Trader Joe’s, Target, or Costco in bulk.