In trading on Wednesday, shares of the PowerShares WilderHill Clean Energy Portfolio ETF ( PBW) entered into oversold territory, changing hands as low as $6.21 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 PowerShares WilderHill Clean Energy Portfolio, the RSI reading has hit 28.9 — by comparison, the RSI reading for the S&P 500 is currently 49.1. A bullish investor could look at PBW's 28.9 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), PBW's low point in its 52 week range is $4.79 per share, with $8.02 as the 52 week high point — that compares with a last trade of $6.22. PowerShares WilderHill Clean Energy Portfolio shares are currently trading down about 2.8% on the day.