Like the other poster said for Sunoco, same holds true for Chevron. The limit is 20c/gallon saving which doesn't help me since the Costco prices are better by 30c+/gallon.
I did get 1000 points (10 rewards) by buying the right $500 VGC but while using it at Chevron it is capped to 20c/2 rewards. I still have the balance of 8 rewards. Though not useful for me, seems like a decent stack for those with safeway gas stations.