In trading on Tuesday, shares of Approach Resources Inc ( AREX) entered into oversold territory, changing hands as low as $17.7501 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 Approach Resources Inc, the RSI reading has hit 29.2 — by comparison, the universe of energy stocks covered by Energy Stock Channel currently has an average RSI of 38.1, the RSI of WTI Crude Oil is at 29.6, and the RSI of Henry Hub Natural Gas is presently 39.4. A bullish investor could look at AREX'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), AREX's low point in its 52 week range is $17.59 per share, with $31.67 as the 52 week high point — that compares with a last trade of $18.11. Approach Resources Inc shares are currently trading off about 13.2% on the day. According to the ETF Finder at ETF Channel, AREX makes up 1.12% of the SPDR S&P Oil & Gas Exploration & Production ETF ( XOP) which is trading lower by about 2.9% on the day Tuesday.