Fuel Rewards Network offers about 1% for shopping online, e.g., I bought $36 worth of clothes from Load and Taylor via their shopping mall, it gave me 10 cent. The calculation goes like this: $36 * 3 / 1000 = $0.108 rounded down to $0.10 which is 10 cent per gallon gas discount. If I buy 10 gallon of gas, that’s $1.00 discount. $1 divide by $36 which comes out by 3%. Note typically shopping mall earning rate is 1 instead of 3, so in the example above, I will earn 3.6 cent per gallon gas discount, instead of 10 cent.
Another example, I shopped at gap via FRN, bought $50 apparel. It gave me 10 cent also (2x earning rate instead of 3x at L&T). This is lower than the gap rebate one can get from ebates right now (typically 2%, now at 8%). I mean 3% or 2% vs. 8%. So the bottom line is we can use this calculation to maximize the cash back (rebate).
Btw, FRN is free to join, and as a minimum it offers 3 cent discount for gas purchase, so in other words about 1% in addition to whatever the credit card offers (in my case, I use Sams Club mastercard or the Pentagon Reward visa, both offer 5% cash/points back).
Back to the topic, I think it’s worth to join FRN since we already spend money on shopping or dining, and those activities adds up to gas savings, in addition to the regular credit card cashback/points we get. Don’t spend to get the points though
(Update 09-20-15) Other two ways I got discount for gas purchase. I use both Sam’s Club MasterCard and PenFed Rewards visa card, both gives 5% cash (points) back, which is unlike some of those rotational 5% reward cards (e.g., Chase Freedom, Discover Cash Bonus). Sometimes it’s hard to keep track of those quarterly rotational promotion. This is also higher than 3% cashback from Amex Costco Card. PenFed also offers 3% for supermarket and grocery shopping. And Sam’s Club MasterCard offers 3% on restaurant purchase.