In trading on Thursday, shares of Century Aluminum Co. ( CENX) entered into oversold territory, changing hands as low as $11.01 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 Century Aluminum Co., the RSI reading has hit 29.9 — by comparison, the universe of metals and mining stocks covered by Metals Channel currently has an average RSI of 45.2, the RSI of Spot Gold is at 44.2, and the RSI of Spot Silver is presently 49.3. A bullish investor could look at CENX's 29.9 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), CENX's low point in its 52 week range is $11.01 per share, with $31.75 as the 52 week high point — that compares with a last trade of $11.52. Century Aluminum Co. shares are currently trading down about 6.3% on the day. According to the ETF Finder at ETF Channel, CENX makes up 2.81% of the SPDR S&P Metals and Mining ETF ( XME) which is trading lower by about 0.5% on the day Thursday.