Kroger & its subsidiary brands are offering 4X fuel rewards on select gift cards through 8/11/15.
While variable load cards are excluded, fixed value Visa & Mastercard gift cards along with a variety of merchant gift cards are normally eligible. (Confirm the terms in your local store.) Generally the highest fixed value cards Visa & Mastercard gift cards available come in $100 denominations for a $5.95 fee.
As I wrote about a few weeks ago, Kroger also has a number of digital coupons for instant discounts on cards for eBay, Gap and other merchants. Both the 4X fuel points and the discounts should stack.
Update: Tjp74 mentioned in the comments that his purchases have been earning 5X fuel points. According to Chuck from Doctor of Credit, fuel points are given based on the face value of the cards, so a $40 purchase of $50 worth of eBay gift cards earns 200 points.
HT: Ian @rotisp on Twitter