In trading on Thursday, shares of the iShares U.S. Utilities ETF (IDU) entered into oversold territory, changing hands as low as $131.75 per share. We define oversold territory using the Relative Strength Index, or RSI, which is a technical analysis indicator used to measure momentum on a scale of zero to 100. A stock is considered to be oversold if the RSI reading falls below 30.In the case of iShares U.S. Utilities, the RSI reading has hit 29.4 — by comparison, the RSI reading for the S&P 500 is currently 69.9. A bullish investor could look at IDU's 29.4 reading as a sign that the recent heavy selling is in the process of exhausting itself, and begin to look for entry point opportunities on the buy side. Looking at a chart of one year performance (below), IDU's low point in its 52 week range is $120.00 per share, with $142.50 as the 52 week high point — that compares with a last trade of $132.60. iShares U.S. Utilities shares are currently trading off about 0.8% on the day.