Tim Cook, chief executive officer of Apple Inc., waves after speaking during an event at the Steve Jobs Theater in Cupertino, California, U.S., on Tuesday, Sept. 12, 2017.

In the technology sector, the biggest keep getting bigger — a lot bigger.

The 10 largest U.S. tech firms by revenue are expected to post aggregate sales of more than $1 trillion this year, possibly for the first time, an analysis of Wall Street estimates shows.

The combined revenue of these giant companies is seen rising by 15.7 percent, or $146 billion, to $1.078 trillion in 2018, based on the average estimates of stock analysts compiled by Thomson Reuters.

The figures show that the leaders of the tech industry are, on average, still growing at a robust pace even after eight consecutive years of U.S. economic growth.

The sector growth expectations also help explain why the 2017 performance of the Nasdaq 100 Index, representing the largest tech firms by market capitalization, outpaced the returns of both the broader Nasdaq Composite Index and .

The NDX rose 30 percent last year, while the Nasdaq Composite climbed 28.2 percent and the S&P 500, 19.4 percent.