U.S. digital advertising revenues accounted for $15.9 billion in 2016’s first quarter, according to a report by ad organization the Interactive Advertising Bureau.

Those numbers are the highest first quarter on record for the industry, and represent a 21-percent climb in Internet ad revenues from 2015’s Q1 figures of $13.2 billion. That year-over-year surge is the sharpest first quarter uptick seen in four years, according to the IAB.

The numbers follow 2015’s record breaking fourth-quarter revenues of $17.4 billion, which resulted in a historic $59.6 billion in industry revenues for that year. The IAB in December 2015 also reported that U.S. advertising revenues had totaled $15 billion in 2015’s third quarter, at that time the highest quarter since the research organization began tracking this data in 1996.

The findings appear in the IAB’s latest Internet Advertising Report, a quarterly estimate of U.S. interactive advertising revenues. That report is sponsored by the IAB and conducted by PricewaterhouseCoopers US.

Quarterly Revenue Growth Trends, 1996 - 2016