In trading on Wednesday, shares of the SPDR S&P Oil & Gas Equipment & Services ETF ( XES) entered into oversold territory, changing hands as low as $42.75 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 SPDR S&P Oil & Gas Equipment & Services, the RSI reading has hit 29.2 — by comparison, the RSI reading for the S&P 500 is currently 49.4. A bullish investor could look at XES's 29.2 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), XES's low point in its 52 week range is $39.54 per share, with $49.63 as the 52 week high point — that compares with a last trade of $42.88. SPDR S&P Oil & Gas Equipment & Services shares are currently trading down about 0.7% on the day.