Google announced they have been testing offering a business credit card for AdWords customers to buy AdWords ads with.
Google said, "to make it easier for small businesses to pay for their AdWords campaigns and track their spending, last July we piloted AdWords Business Credit in the US, a credit card specifically for AdWords." They said the pilot worked well, they are expanding it to the UK.
You can learn more about the UK offering at this page. But it is a bit hard for US advertisers to learn about the US version.
I found this FAQ page on how to apply for the US version of the credit card. It basically takes you to this page where you can enter your AdWords account ID and then start the application process there.
The site and credit card is technically not run by Google in the US or UK, in the US it is run by the World Financial Capital Bank and in the UK it is run by Barclay.
A WebmasterWorld thread has a lot of skeptical AdWords advertisers, however, one AdWords advertiser has the credit card and said he likes it because it gives him a larger credit line. He wrote:
I'm in the U.S. and my AdWords credit card has a $15K limit on it, way more than my regular credit card.
Are you going to apply?
Forum discussion at WebmasterWorld.
