In trading on Thursday, shares of the iShares U.S. Oil Equipment & Services ETF ( IEZ) entered into oversold territory, changing hands as low as $70.601 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. Oil Equipment & Services, the RSI reading has hit 28.8 — by comparison, the RSI reading for the S&P 500 is currently 32.2. A bullish investor could look at IEZ's 28.8 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), IEZ's low point in its 52 week range is $59.01 per share, with $77.98 as the 52 week high point — that compares with a last trade of $70.66. iShares U.S. Oil Equipment & Services shares are currently trading off about 1.1% on the day.