Twitter and American Express have expanded on their longstanding partnership to offer a unique e-commerce service to Amex cardholders that both parties hope will convert Twitter hashtags into purchases.

The collaboration uses Amex’s Card Sync technology, and card members who connect their cards to their Twitter accounts can benefit from special offers on products, including gift cards, Kindle Fire tablets and more.

Here’s how it works. After cardholders have synced an eligible American Express card with their Twitter profile, they watch their Twitter feed for special deals from @AmexSync. Once they see an offer that they like, they simply tweet the relevant hashtag to participate.

Check the video below for more details:

The partnership began yesterday, and Amex card members have already been able to “tweet to buy” $25 Amex gift cards for just $15 by using the #BuyAmexGiftCard25 hashtag. Further offers from Amazon, including a Kindle Fire HD at $50 off the RRP, Sony, Urban Zen and Xbox will be released later this week.

“We’re convinced that commerce is going to be one of the areas (for which) advertisers are going to start using our platform,” said Joel Lunenfeld, Twitter’s vice president of global brand strategy, in an interview.

(Source: WSJ.)