Other social networks including Facebook could also generate extra revenue as users pay for products online
Twitter and American Express say they are working on a "pay by tweet" system that would let accredited users pay for real or virtual items via the microblogging service.
That could also generate an extra lucrative source of revenue for Twitter, which has recently hiked prices on its "promoted trend" service as it looks towards a potential flotation in 2014.
According to the Wall Street Journal, the new service with Amex would let people who link their cards to their Twitter accounts buy products simply by tweeting in response to special offers made over the service.
That could generate a chunk of payments for Twitter if it takes a slice of those purchases. But the service, with more than 200 million users worldwide, is also beginning to ratchet up prices for reaching users: last week it raised the price of a "promoted trend" – visible to many users as they look to see what topics are generating the most interest – to $200,000 per day.
Twitter generated an estimated $350m in revenues in 2012, and its growth and increasing interest among advertisers seeking to place promoted tweets and trends could double that in 2013.
American Express is creating similar card connection systems to work with Facebook, Microsoft's Xbox Live service and the location-based service FourSquare. "Hundreds of thousands" of people have connected their cards to those services, it said: in those, a card could be used to buy virtual goods through Facebook apps, or games and films on the Xbox Live service.