Growth stocks outperformed value stocks in May at every capitalization tier, according to the Russell Investment Group's family of U.S. equity indexes. At the end of May, the large-cap Russell 1000 Growth Index, with returns of 4.84%, beat the Russell 1000 Value Index, which returned 2.41%.

"Growth stocks rallied somewhat in May but still lag behind value for the year," said Paola Nealon, manager research analyst at Tacoma, Wash.-based Russell Investment. "We'll see if a new trend develops, but growth investors did receive a little encouragement in May."

Overall, each of Russell's 22 U.S. stock indexes showed strong performances in May, ranging from the Russell 2000 Growth Index, which returned 7.05%, to the Russell Top 200 Value Index with a 1.61% return. The broad market Russell 3000 Index reflected a 3.79% gain for the month, as about 80% of the companies turned in a positive performance.

"The declining price of oil seems to have benefited the broad market," said Nealon. "For the Russell 1000, the tech sector led the way with a 9.35% return for the month. This relatively strong performance isn't surprising given the inverse relationship the technology sector has with the price of oil."

Nealon noted that 60 technology companies in the Russell 3000 each gained at least 20% for the month.

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