18 Overbought Stocks to Sell Now

(Update with information about Netezza's buyout and impact on Radware.)

NEW YORK (TheStreet) -- Despite a few ups and downs the major stock indexes are up about 1% year-to-date. Among the gains -- of which there were many -- a number of specific stocks are now considered overbought and may be ripe for a sell.

A stock is generally considered overbought when high demand unjustifiably pushes its price higher than its underlying fundamentals support. It may also mean the stock's price has risen so much, and usually on high volume, that an oscillator's upper boundary has been reached, according to Investopedia. That usually indicates the equity's price is overvalued and due for a pullback.

Taking this into consideration, TheStreet looked at the overall equity market and screened for stocks with a price-earnings ratio greater than 50 and a weighted alpha greater than 100, according to data from Barchart.

P/E ratios measure a stock's current price compared to its per-share earnings. The metric points to a stock's most fundamental level of valuation, explained Nicholas Colas, chief market strategist at ConvergEx Group. Lower P/Es indicate lower levels of valuation and better opportunity; higher P/Es mean good news about the stock has already been baked into its price.

Weighted alpha is the measure of how much a stock gained or lost over the past year with an emphasis on the most recent price activity. If the stock is up it will have a positively weighted alpha. If the stock price is unchanged its weighted alpha will be smaller. A stock price loss will yield a negatively weighted alpha. Barchart weights the metric, assigning more weight to recent activity, and less to activity at the beginning of the period. This rear-looking indicator demonstrates how much outperformance has already occurred, Colas said.

"It's very tricky to know if all this means you should sell or not," Colas said. "If you own a stock on this list, you likely already booked a gain on it and would be wise to think about when you want to sell. If you don't already own it you will have a higher level of risk buying it now because so many good expectations are already priced in for future results."

In other words, the market already seems to know the company's positive traits. After all, stock picking is all about matching what you know with what the market knows, and trying to outpace.

Here, then, is TheStreet's list of 18 most overbought stocks, from the least overbought to the most.