The S&P 500 rose 0.2% to 3,396.27 in midday trading.
The Dow Jones Industrial Average increased 0.2% to 27,844.04.
The Nasdaq climbed 0.4% to 11,251.30.
The yield on a 10-year Treasury bond was down 0.3% to 0.667%.
The price of gold fell 2.1% to $1,972 an ounce.
Crude oil was flat at $42.88 a barrel.
Newport Beach-based Clean Energy Fuels Corp. (Nasdaq: CLNE) rose 5.3% to $2.97 and a $589 million market cap. Shares of Clean Energy, which supplies renewable natural gas, have almost tripled since their 52-week low of $1.05 in March.
Emerald Holdings Inc. (Nasdaq: EEX) increased 4.7% to $2.88 and a $206 million market cap. The stock price of the San Juan Capistrano producer of trade shows is still down about 75% since early February.