For those who may be interested, right now it looks like the best cash back card on offer which expressly covers marinas & marina gas in their terms conditions is the Bank of America Customized Cash Reward card, which offers 3% back up to $2500 spent per quarter (1% thereafter). Thus if you spend $2500 in gas in a quarter, you get back $75, plus there’s a $200 sign up bonus. It also offers 2% back on groceries and warehouse club purchases (up to that same $2500 limit as the gas) and 1% everything else & all purchases over the $2500 per quarter limit. Every other card I found said the “MCC” (Merchant Categorization Code) assigned to the business had to be for a gas station, and one defined the codes as MCC 5542 & 5552. So if you are interested in those cards, you can ask the place where you get gas what code they are (apparently it’s a code used by all major credit cards, ie. AMEX, Visa, MC). Hope this is helpful to someone!