The five-month plunge that lopped 29 percent from the price of oil has left energy stocks with the weakest influence on U.S. equities in nine years. For investors tiring of volatility, that’s a good thing.

Oil and gas producers in the Standard & Poor’s 500 Index plunged as much as 20 percent since June, squeezing their share of the gauge to 8.9 percent, the smallest since 2005. That’s down from 16 percent in 2008 and put them as the seventh among 10 industries, data compiled by Bloomberg show.

Liberating the biggest stock measure from the vicissitudes of commodity markets will reduce volatility and attract investors as industries such as technology and health care thrive, said Brad McMillan of Commonwealth Financial Network. Energy shares fell about twice as fast as the full index during the September-October retreat as concern over a global economic slowdown and a glut of supply sent oil to the longest slump in almost three decades.

“Oil prices have been notoriously volatile for many years,” McMillan, chief investment officer of Waltham, Massachusetts-based Commonwealth Financial Network, which oversees $86 billion, said in a phone interview. “Because there is such a knock-on effect, the less important energy becomes to the index, that’d probably reduce market volatility as a whole going forward.”

Oil Effect

Oil’s slide pushed energy shares down 20 percent over the four months through October, contributing almost half of the 4.3 percent loss in the S&P 500. Without energy, the broad index’s decline over the stretch would have been 2.4 percent, according to data compiled by S&P Dow Jones Indices.

The equity market has since recovered all the losses as better-than-forecast corporate earnings and improved data on employment and manufacturing sent the benchmark index to all- time highs. The S&P 500 Energy Index is still 15 percent below its June peak, hurt by crude prices that broke $75 a barrel for the first time since 2010. Futures on the broader gauge fell 0.5 percent at 9:40 a.m. in London today.

“Investors should be happy that energy is such a low weight in the S&P because it obviously has a lot less impact than it would have been,” Wayne Wilbanks, who oversees about $2.5 billion as chief investment officer at Norfolk, Virginia- based Wilbanks, Smith & Thomas Asset Management LLC, said by phone. “The quick rebound in the market was in part fueled by people stopping and then going, ‘You know what? Oil staying at $75 -- that’s great for everyone else.’”

GDP Impact

U.S. gross domestic product will get a net 0.5 percentage point boost over the next year from crude’s retreat, taking into account a pickup in consumer spending and cutbacks in business investment by the oil industry, according to a forecast by JPMorgan Chase & Co. Estimates from Goldman Sachs Group Inc. put the increase at 0.1 point in 2015.