Corporate insiders sell their own companies' stock for a number of reasons. ¿

They might need the cash for a big personal purchase such as a new house or yacht, or they might need the cash to fund a charity. Sometimes they sell as part of a planned selling program that they have put in place for diversification purposes, which allows them to sell stock in stages instead of selling all at one price.

Other times they sell because they think their stock is overvalued and the risk/reward is no longer attractive. Some even dump their own stock because they have inside knowledge that a competitor is eating their lunch and stealing market share. ¿

But insiders usually buy their own shares for one reason: They think the stock is a bargain and has tremendous upside.

The key word in that last statement is "think." Just because a corporate insider thinks his or her stock is going to trade higher, that doesn't mean it will play out that way. Insiders can have all the conviction in the world that their stock is a buy, but if the market doesn't agree with them, the stock could end up going nowhere. Also, I say "usually" because sometimes insiders are loaned money by the company to buy their own stock. Those loans are often sweetheart deals and shouldn't be viewed as organic insider buying.

At the end of the day, it's institutional money managers running big mutual funds and hedge funds that drive stock prices, not insiders. That said, many of these savvy stock operators will follow insider buying activity when they agree with the insider that the stock is undervalued and has upside potential. This is why it's so important to always be monitoring insider activity but twice as important to make sure the trend of the stock coincides with the insider buying.

Recently, a number of companies' corporate insiders have bought large amounts of stock. These insiders are finding some value in the market, which warrants a closer look at these stocks.

Phillips 66

One energy player that insiders are snapping up a massive amount of stock in here is Phillips 66(PSX) - Get Report , which operates as an energy manufacturing and logistics company. Insiders are buying this stock into modest weakness, since shares have fallen by 7.2% over the last three months.

Phillips 66 has a market cap of $41.5 billion and an enterprise value of $44.7 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 9 and a forward price-to-earnings of 10.8. Its estimated growth rate for this year is 16.2%, and for next year it's pegged at -6.5%. This is not a cash-rich company, since the total cash position on its balance sheet is $4.82 billion and its total debt is $8.95 billion. This stock currently sports a dividend yield of 2.9%.

A beneficial owner just bought 1,645,887 shares, or about $126 million worth of stock, at $76.44 to $78.01 per share. This same beneficial owner also just bought 1,741,210 shares, or about $132 million worth of stock, at $75.82 to $77.17 per share.

From a technical perspective, Phillips 66 is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending over the last month and change, with shares falling off its high of $94.06 to its recent low of $74.37 a share. During that downtrend, shares of Phillips 66 have been making mostly lower highs and lower lows, which is bearish technical price action. That said, this stock has now started to bounce to the upside off that $74.37 low, and it's beginning to move within range of triggering a near-term breakout trade.

If you're bullish on Phillips 66, then I would look for long-biased trades as long as this stock is trending above that recent low of $74.37 or above more key support at $73.48 a share and then once it breaks out above some near-term overhead resistance levels at $80 to its 200-day moving average of $80.87 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 3.21 million shares. If that breakout develops soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $84 to $85, or even its 50-day moving average of $86.54 a share.

Array BioPharma

Another biopharmaceutical player that insiders are loading up on here is Array BioPharma(ARRY) - Get Report , which focuses on the discovery, development, and commercialization of small molecule drugs to treat patients with cancer in North America, Europe, and the Asia Pacific. Insiders are buying this stock into large weakness, since shares have dropped sharply by 27.3% over the last three months.

Array BioPharma has a market cap of $510 million and an enterprise value of $447 million. This stock trades at a premium valuation, with a trailing price-to-earnings of 31.6. Its estimated growth rate for this year is -785.7%, and for next year it's pegged at -10.4%. This is a cash-rich company, since the total cash position on its balance sheet is $159.30 million and its total debt is $108.81 million.

A beneficial owner just bought 925,000 shares, or about $3.39 million worth of stock, at $3.54 per share.

From a technical perspective, Array BioPharma is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending over the last month and change, with shares moving lower from its high of $5.20 to its recent low of $3.40 a share. During that downtrend, shares of Array BioPharma have been consistently making lower highs and lower lows, which is bearish technical price action. That said, this stock has started to bounce modestly off its new 52-week low of $3.40 a share, and it's beginning to trend within range of triggering a near-term breakout trade.

If you're in the bull camp on Array BioPharma, then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $3.40 a share and then once it breaks out above some near-term overhead resistance at $3.75 a share and above both its 20-day moving average of $4.10 and its 50-day moving average of $4.23 a share with volume that registers near or above its three-month average action of 2.70 million shares. If that breakout kicks off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $4.50 to $4.75, or even $5.20 to $5.50 a share.

Conn's

One electronics stores player that insiders are active in here is Conn's(CONN) - Get Report , which operates as a specialty retailer of durable consumer goods and related services in the U.S. Insiders are buying this stock into big weakness, since shares have traded off by 36.1% over the last three months.

Conn's has a market cap of $494 million and an enterprise value of $1.5 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 12.4 and a forward price-to-earnings of 7.9. Its estimated growth rate for this year is -33.3%, and for next year it's pegged at 67.2%. This is not a cash-rich company, since the total cash position on its balance sheet is $109.07 million and its total debt is $1.16 billion.

A beneficial owner just bought 90,000 shares, or about $1.50 million worth of stock, at $16.76 per share. That same beneficial owner also just bought 30,000 shares, or about $502,000 worth of stock, at $16.76 per share.

From a technical perspective, Conn's is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending badly over the last month and change, with shares falling sharply off its high of $28 to its new 52-week low of $14.68 a share. During that downtrend, shares of Conn's have been making mostly lower highs and lower lows, which is bearish technical price action. That move has now pushed this stock into extremely oversold territory, since its current relative strength index reading is 22. Oversold can always get more oversold, but it's also an area where a stock can make a powerful bounce higher from if buyers step in.

If you're bullish on Conn's, then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $14.68 or above some key previous support at $14.02 a share and then once it breaks out above some near-term overhead resistance levels at $16 to $17 a share with high volume. Look for a sustained move or close above those levels with volume that registers near or above its three-month average action of 819,627 shares. If that breakout materializes soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $20 to its 20-day moving average of $21.74, or even its 50-day moving average of $23.37 a share.

Acadia Pharmaceuticals

One biopharmaceutical player that insiders are in love with here is Acadia Pharmaceuticals(ACAD) - Get Report , which focuses on the development and commercialization of small molecule drugs that address unmet medical needs in neurological and related central nervous system disorders. Insiders are buying this stock into notable weakness, since shares have dropped by 17.5% over the last three months.

Acadia Pharmaceuticals has a market cap of $3 billion and an enterprise value of $2.4 billion. This stock trades at a premium valuation, with a price-to-book of 12. Its estimated growth rate for this year is -60%, and for next year it's pegged at 15.1%. This is a cash-rich company, since the total cash position on its balance sheet is $240.69 million and its total debt is zero.

A director just bought 2,586,206 shares, or about $74.99 million worth of stock, at $29 per share.

From a technical perspective, Acadia Pharmaceuticals is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending over the last two months and change, with shares moving lower off its high of $43.30 to its new 52-week low of $25.69 a share. During that downtrending, shares of Acadia Pharmaceuticals have been making mostly lower highs and lower lows, which is bearish technical price action. That move has now pushed this stock into extremely oversold territory, since its current relative strength index reading is 25. Oversold can always get more oversold, but it's also an area where a stock can experience a powerful bounce higher from if buyers show up.

If you're bullish on Acadia Pharmaceuticals, then I would look for long-biased trades as long as this stock is trending above some its new 52-week low of $25.69 or above $24 a share and then once it breaks out above some near-term overhead resistance levels at $29 to $29.33 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 1.32 million shares. If that breakout kicks off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $32.50 to its 20-day moving average of $33.10, or even its 50-day moving average of $35.24 a share.

Tangoe

One final stock with some big insider buying is business software and services player Tangoe (TNGO) , which provides connection lifecycle management software and related services to enterprises and service providers worldwide. Insiders are buying this stock into massive weakness, since shares have plunged by 35.7% over the last six months.

Tangoe has a market cap of $320 million and an enterprise value of $293 million. This stock trades at a reasonable valuation, with a forward price-to-earnings of 21.3. Its estimated growth rate for this year is -51.4%, and for next year it's pegged at 11.8%. This is a cash-rich company, since the total cash position on its balance sheet is $36.56 million and its total debt is $5.04 million.

A beneficial owner just bought 665,798 shares, or about $5.51 million worth of stock at $8.12 to $8.33 per share. From a technical perspective, Tangoe is currently trending above its 50-day moving average and below its 200-day moving average, which is neutral trendwise. This stock has been consolidating and trending sideways over the last month and change, with shares moving between $7.85 on the downside and $8.99 on the upside. Shares of Tangoe are now starting to bounce off the lower-end of its recent range, and it's beginning to move close to triggering a major breakout trade above the upper-end of its recent sideways trending chart pattern.

If you're bullish on Tangoe, then I would look for long-biased trades as long as this stock is trending above some near-term support at $7.85 or above more support at $7.50 a share and then once it breaks out above its 20-day moving average of $8.47 and then above more key resistance levels at $8.84 to $8.99 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average volume of 359,289 shares. If that breakout takes hold soon, then this stock will set up to re-fill some of its previous gap-down-day zone from August that started near $11.50 a share.

Disclosure: This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.