Americans are spending an average of two hours per day playing games on mobile devices, up from an hour and 20 minutes in 2012, according to a survey conducted late last year by the NPD Group.
The research firm attributed the growth to rising tablet sales and technological improvements, calling those devices "central to the mobile gaming story." Mobile gamers are more likely to make purchases on tablets than on smartphones or iPod Touches, the survey found.
The most active mobile gamers, measured against usage of other types of apps on mobile devices, were children age 2 to 12, who played an average of five games per day. However, that group was overshadowed in spending on games by adults age 25 to 44.
"This group [adult gamers] also tends to be the decision-makers for their young children's gaming experiences, making them a prime target for developers and marketers alike," NPD analyst Liam Callahan said in a press release.
Read MoreTaylor Swift's social media hijacked
The 5,566 online survey respondents did not report spending less time on console and computer gaming than in the past, and 80 percent of them also played on those platforms. However, mobile devices were where they spent the greatest proportion of their gaming time on average.
CNBC's parent NBC Universal is an investor in Re/code's parent Revere Digital, and the companies have a content-sharing arrangement.