As of today, the Technology sector remains the biggest sector in the S&P 500, but its weighting has fallen in 2012 as other sectors have taken share. The Technology sector currently makes up 18.95% of the S&P 500, while it ended 2011 at 19.02%.
The Financial sector has gained by far the most market share in 2012. At the end of 2011, the Financial sector made up 13.43% of the S&P 500. It currently makes up 15.63%. This move has closed the weighting gap between Technology and Financials by 2.27 percentage points. If this happens again in 2013, the two sectors will have pretty similar weightings.
Consumer Discretionary, Health Care and Materials are the other three sectors that have seen their S&P 500 weightings increase in 2012.
On the downside, the Energy sector has lost the most share at -1.22 percentage points. While Energy ended 2011 as the third biggest sector in the market, it is now just the fifth biggest. Consumer Staples also lost quite a bit of share at -0.89 percentage points.