Amazon, Microsoft and Alphabet are locked in a tight race to become the second publicly-listed US company to reach a one-trillion-US-dollar stock market value after Apple became the first to touch the 13-digit milestone.

Wall Street’s optimism about last year’s 10th anniversary iPhone, coupled with record share buybacks, have propelled Apple’s stock 34 percent higher over the past 12 months, pushing the company’s stock market value above one trillion US dollars on Thursday.

The Cupertino, California company’s shares added another 0.3 percent on Friday, putting its market capitalization at 1.005 trillion US dollars.

Apple’s 12-month gain is far better than the S&P 500’s 14 percent increase over the past year, but it pales beside Amazon’s astounding 85 percent surge, propelled by the online retailer’s and cloud computing heavyweight’s scorchingly fast revenue and profit growth.

Amazon is now the second-largest publicly-listed US company, with a market capitalization of 889 billion US dollars, followed closely by Alphabet and Microsoft, at 856 billion US dollars and 830 billion US dollars respectively.

Google-owner Alphabet’s stock has risen 32 percent over the past 12 months, and is up nearly 18 percent in 2018.

Together with Facebook, the five largest US companies account for 15 percent of the S&P 500.

Synovus Trust portfolio manager Dan Morgan said he owns shares of Amazon mostly because of its dominance of the cloud computing industry, a business that grew 42 percent in the June quarter and provided most of Amazon’s operating profits.

“Of the three companies, I’d say Amazon will get to one trillion US dollars next,” Morgan said.

Average analyst price targets put Apple’s stock market value at 1.05 trillion US dollars, Amazon at 1.02 trillion US dollars, Alphabet at 970 billion US dollars and Microsoft at 953 billion US dollars, according to Thomson Reuters data.

To be sure, past stock gains are not a reliable predictor of future performance, and the surge in Amazon shares in recent years has been exceptional by most standards. But Amazon’s market capitalization would overtake Apple’s later in 2018 if both companies shares were to continue their 12-month growth pace.