It is estimated that U.S. mobile app-installed ads accounted for 30% of all mobile advertising revenue in 2014, and will top $4.6bn in 2016, and over $6.8bn by the end of 2019. Other ways mobile advertising can be purchased include working with a Mobile Demand Side Platform, in which ad impressions are bought in real-time on an Ad exchange. Another report has indicated that worldwide mobile digital advertising spend would reach $184.91 bn in 2018, $217.42 bn in 2019 and $247.36 bn in 2020.