The decade-long bull market, shaken with a wave of volatility in 2018 on a handful of concerns such as a global trade war and rising interest rates, has been criticized for concentrating too much wealth in shares of expensive, high-flying U.S. tech giants. If anything, America's largest technology companies have only gained favor with investors this year, with Amazon.com Inc. (AMZN), Netflix Inc. (NFLX) and Microsoft Corp. (MSFT) responsible for a whopping 71% of the S&P 500's returns year-to-date (YTD) and 78% of the Nasdaq 100's returns, as reported by CNBC. (See also: Best Performing S&P 500 Stocks So Far in 2018.)

E-commerce and cloud computing giant Amazon led the pack, accounting for 35% of S&P 500 gains and 41% of Nasdaq 100 returns so far in 2018. The Seattle-based behemoth continues to enter new markets such and brick-and-mortar grocery and health care, while beefing up its bread-and-butter retail business and public cloud platform, Amazon Web Services (AWS). Shares of Amazon are up 49.1% YTD through Tuesday close at $1,743.07, compared to the S&P 500's 4.5% jump. 

Tech Titans Continue Make Headways in Growth Markets

Netflix, a leader in the burgeoning on-demand video streaming space, has made up 21% of the S&P 500 returns and 21% of Nasdaq 100 gains this year. Closing down about 0.8% on Tuesday at $415.63, Netflix stock reflects a 116.5% gain YTD. The Economist estimates that the Los Gatos, California-based company will shell out between $12 billion and $13 billion on original content this year, compared to the company's previous forecast of $8 billion, far more than any film studio or television company. 

Microsoft has accounted for 15% of S&P 500 growth and 15% of Nasdaq 100 gains in 2018, itself jumping 19.4% YTD at a price of $102.12 per share. The old guard tech titan has been applauded for successfully executing a restructuring of its business away from legacy businesses such as Windows to new high-growth markets like the cloud, artificial intelligence (AI), productivity software and career networking via its LinkedIn platform. 

Apple Inc. (AAPL), Google parent company Alphabet Inc. (GOOGL) and Facebook Inc. (FB) also make up large portions of both indexes, contributing 12%, 8% and 8% to both the S&P 500 and Nasdaq 100 returns YTD, respectively. (See also: 8 Micro-Cap Stocks That Are Beating the Blue Chips.)

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