The video game industry pumps at least $18 billion into the U.S. economy, a study released this week claimed.

Written by a pair from the Brookings Institution and Georgetown University but funded by the Entertainment Software Association (ESA), a game industry group, the study said that 2004 sales directly contributed $10.3 billion to the country's gross national product. Adding in another $7.8 billion for spending on such ancillary products and services as a portion of high definition television sets and part of broadband Internet revenues brings the grand total to $18.1 billion.

"Not only does entertainment software trigger complementary sales, it triggers those complementary sales faster than they would otherwise occur," said the study's authors, Robert Crandall and J. Gregory Sidak. "For example, but for the demand for video games, computer processing would not have developed as quickly."

The two added that although the video game industry supported 144,000 full-time workers in 2004, that number would climb to 250,000 by 2009.

"Clearly, the entertainment software industry is not just about 'fun and games.' It is a serious business. Video games play an important role in maintaining U.S. leadership in information technology, which is critical to the future success of the U.S. economy," Crandall and Sidak wrote.

The study, which can be downloaded in PDF format from the ESA Web site, was released at E3, the video and computer game industry's biggest trade show which opened Wednesday and runs through Friday.