In trading on Wednesday, shares of the iShares U.S. Oil & Gas Exploration & Production ETF ( IEO) entered into oversold territory, changing hands as low as $87.01 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 & Gas Exploration & Production, the RSI reading has hit 29.4 — by comparison, the RSI reading for the S&P 500 is currently 51.5. A bullish investor could look at IEO'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), IEO's low point in its 52 week range is $76.88 per share, with $99.88 as the 52 week high point — that compares with a last trade of $87.50. iShares U.S. Oil & Gas Exploration & Production shares are currently trading down about 1.2% on the day.