Mobile devices will account for 75% of global internet use next year, according to Zenith's new mobile advertising forecasts.
This is expected to reach 79% by 2018 - double the 40% recorded in 2012.
In 2012 just 23% of people in the 60 markets surveyed had a smartphone and 4% had a tablet. Smartphone penetration has now reached 56% and is forecast to rise to 63% by 2018.
Tablet penetration has been much slower, however, with ownership currently standing at 15%. This is expected to reach 17% in 2018.
Consequently, Zenith predicts that mobile advertising will overtake desktop in 2017, increasing its share of global internet advertising to 52% from 44% this year.
In 2018 mobile advertising is expected to account for 60% of all internet advertising, seeing total expenditure reach US$134bn - more than newspapers, magazines, cinema and outdoor advertising put combined.
"Mobile devices are already the primary means of accessing the internet across the world," said Jonathan Barnard, head of forecasting at Zenith.
"Countries in Western Europe, Asia and North America are leading the transition, but mobile technology is spreading rapidly everywhere. Next year mobile devices will become the main vehicle for internet advertising as well."