Monday continued the positive string of stock market performances for 2018, as major benchmarks largely bounced back from losses early in the session to finish with modest gains. Sentiment among investors has been extremely high to start the year, helping to spur advances but also raising concerns that exuberance on Wall Street might be reaching irrational levels. Nevertheless, good news affecting key individual companies helped to support market indexes, and Tesla (NASDAQ:TSLA), Weight Watchers International (NYSE:WTW), and Seagate Technology (NASDAQ:STX) were among the best performers on the day. Below, we'll look more closely at these stocks to tell you why they did so well.

Tesla revs up

Shares of Tesla picked up 6%, bouncing back from subpar performance last week as investors regained confidence in the electric vehicle manufacturer's ability to capitalize on a lucrative market opportunity. Last week, Tesla disappointed investors when it announced fourth-quarter vehicle delivery numbers that included fewer-than-expected Model 3 deliveries. Yet the company argued that focusing on quality and efficiency was smarter than simply getting production numbers up, and although it took a few days, shareholders seemed eventually to buy into that argument. With potential not only for the Model 3 but also battery production and other groundbreaking innovations, Tesla still captures the imagination of forward-looking enthusiasts -- even if some say its stock price has already gotten ahead of itself.

Blue Tesla Model 3 driving on an open road on a rolling prairie in front of a hazy background.

Image source: Tesla.

Oprah speculation lifts Weight Watchers

Shares of Weight Watchers International climbed 12% after investors responded positively to a speech given by company spokesperson and major shareholder Oprah Winfrey at the Golden Globe Awards Sunday night. Winfrey has denied that she intends to run in the 2020 presidential election, but some believe that she might change her mind in the next couple of years. Given that Weight Watchers has now identified itself very closely with Winfrey, many shareholders are tying the futures of the two together. Investors still need to watch fundamental business performance at this key time of the year for the weight-loss business, but publicity linked to Winfrey could help gain attention for Weight Watchers.

Seagate ripples higher

Finally, shares of Seagate Technology rose 7%. The data-storage specialist became the latest stock to jump in response to cryptocurrency fever, as rumors surfaced that Seagate might have a significant position in the company behind the rising crypto play Ripple. The website for the cryptocurrency company identified Seagate as an early investor in past rounds of capital raising, although it doesn't state whether Seagate retained its interest. Ripple has recently challenged ethereum for the No. 2 spot behind bitcoin in terms of total market value of outstanding coin, with dramatic gains in 2017 that dwarfed what the other two cryptocurrencies produced. Yet without confirmation, any gains from speculation could easily reverse themselves once the facts come out.

Dan Caplinger has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Tesla. The Motley Fool has a disclosure policy.