Mike is the owner of CreditCardForum.com, which is a forum and blog for discussing credit-related topics. Recently, he’s been working on a list of the best gas credit cards and his most recent credit card review was for the Chase Ink card. But no matter what rewards a credit card offers, he urges anyone that doesn’t pay their balance in full each month to avoid them completely!

Thanks to all the ruckus in Egypt and the Middle East, gas prices have started to climb again… the timing couldn’t be worse considering how shaky our economy still is! Of course, gas stations and credit card companies are trying to take advantage of this situation, by using it as a marketing ploy to get you to sign up for their gas cards. However that may be a bad idea, because there are a lot of gotcha’s when it comes to even the best gas credit cards.

Gotcha #1: Caps on rewards

As a rule of thumb, if a credit card claims high cash back on gas, you can bet there is some fine print behind the offer. It’s just not possible for them to make a profit by offering an unlimited 5% on gas, considering that the transaction fees they earn are only 2% to 3%.

For example, the card from Phillips 66/Conoco/76 does give a rebate of 4% at their stations, but there is a maximum of $50 in rewards that will be given each billing cycle. If all you buy is gas, obviously it’s unlikely you will ever reach that amount. However, if you spend a lot on other purchases it could be a problem. Or maybe you are someone that goes through a lot of fuel for work. I have a buddy that has a snowplowing business and goes through a lot of fuel on his diesel truck – for him the cap might be reached during the winter months. He considered the Chase Ink card instead, but even with that it looked like he would still exceed the monthly cap.

Not all of them have caps, but almost all of the major credit cards that are not affiliated with a gas station do cap your gas rewards. For example, the Discover Open Road gives 2% on the first $250 spent per month on gas and restaurants. The Chase Freedom credit card gives 5% but for 2011 that is only given during July thru Sept. and the 5% only applies to the first $1,500 in combined spending for gas, airlines, and hotels during that entire period.

Gotcha #2: Not all gas purchases qualify

Whenever you look at ads for gas credit cards, you will notice the phrase “on qualifying purchases only” but what does that mean? Well, the exclusions vary by card but here are the 4 most common things I have seen that you need to look out for:

1. Pay at the pump vs. inside: Some gas cards only give you the higher rebate if you pay at the pump.

2. Type of fuel purchased: There are a few that exclude diesel fuel from the rebates.

3. Participating stations: This especially applies to the gas credit cards that are affiliated with a specific station. Often times the rebate only applies to their “participating stations” and you will have to check with them to ensure the station you go to participates.

4. Warehouse clubs: Typically the higher rebate does not apply to gas purchases made at Sams Club, Costco, etc.

Gotcha #3: Expiration of rewards

The credit card industry is moving away from expiring rewards because it’s such a sore point among consumers, but there are still many out there that do it.

In the past, I have come across station-branded cards where the rewards expire in as little as 12 months after you earn them. If they have a minimum redemption amount (say, $50) this can be a problem because you may not even earn $50 in rewards over the period of a year if you don’t drive much! And hence, some of your rewards may expire before you even have a chance to use them! So always check the fine print to see if/when rewards will expire.