Market research firm The NPD group has claimed that PC game digital sales for the first six months of 2010 have outgrown retail.
Digital sales in the US reached 11.2 million units, survey findings estimated, while bricks and mortar retail totally 8.2 million.
But overall PC revenues declined 21 per cent, and unit sales by 14 per cent, the firm claimed.
The NPD does not have access to the various download services' sales figures, with both Steam and Blizzard recently confirming to GamesIndustry.biz that they have not provided any data to the analyst.
Last week, EA boss John Riccitiello also claimed NPD reports do not accurately reflect the download market.
Nonetheless, the NPD used "weighted and projected" consumer surveys to draw up a list of what it claims are the most successful download services.
Steam was an unsurprising number one, with Big Fish Games apparently ruling the casual sector.
Direct2Drive, EA, Worldofwarcraft.com and Blizzard.com constituted the remainder of the core games top five. Non-appearing services such as Impulse and GamersGate have previously questioned the accuracy of NPD's download service chart.
"One major finding from this latest report is that the 'big got bigger' in the first half of 2010, with both Steam and Bigfish capturing a bigger share of full-game PC games digital download sales than they did last year," said NPD analyst Anita Frazier.
"The overall decline of PC games when combining sales via both digital downloads and physical retail sales is impacted by the expansion of social network gaming as well as the continued expansion of free game options."