NPD has revealed that US consumers spent around $4.5 to $4.75 billion on "used games, rentals, subscriptions, digital download games, DLC, and mobile apps" in 2009.
Digital content like map packs and other DLC made up the largest chunk of the figure, and helped contribute to $15.0 to $15.25 billion spent on gaming last year.
The other $10.5 million came from physical copies, however the figures do not include money spent on social gaming titles that make use of microtransactions.
"Our expanded estimate of consumer spending reflects the growing number of options to purchase, acquire and interact with video games ranging from GameFly rentals to iPod Touch game apps," says NPD's Anita Frazier.
"Consumer spending on social network games like those offered by Facebook would push this estimate even higher."
The data was pulled from point-of-sale tracking, consumer research and figures culled by NPD retail and its publisher partners.