DELAFIELD, Wis. (Stockpickr) -- 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.

NuStar Energy

One energy stock that insiders are loading up on here is NuStar Energy (NS - Get Report), which is engaged in the terminalling, storage and marketing of petroleum products and the transportation of petroleum products and anhydrous ammonia primarily in the U.S. and the Netherlands. Insiders are buying this stock into decent strength, since shares have moved up 11.8% over the last three months.

NuStar Energy has a market cap of $4.9 billion and an enterprise value of $7.5 billion. This stock trades at a fair valuation, with a trailing price-to-earnings of 30 and a forward price-to-earnings of 21.2. Its estimated growth rate for this year is 23.8%, and for next year it's pegged at 13.8%. This is not a cash-rich company, since the total cash position on its balance sheet is $25.69 million and its total debt is $2.75 billion. This stock currently sports a dividend yield of 6.9%.

A director just bought 74,460 shares, or about $4.54 million worth of stock, at $61.05 per share. This same director also just bought 13,440 shares, or about $826,000 worth of stock, at $61.48 to $61.50 per share.

From a technical perspective, NS is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending very strong for the last three months, with shares moving higher from its low of $50.02 to its recent high of $63.78 a share. During that uptrend, shares of NS have been consistently making higher lows and higher highs, which is bullish technical price action. Shares of NS are now starting to trend within range of triggering a big breakout trade above some key overhead resistance levels.

If you're bullish on NS, then I would look for long-biased trades as long as this stock is trending above its 200-day moving average of $59.50 or its 50-day moving average of $59.17 and then once it breaks out above some key overhead resistance levels at $63.78 to $63.60 a share and then above $64.61 to $65.37 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 volume of 384,832 shares. If that breakout begins soon, then NS will set up to tag or take out $70 a share.

Dominion Resources

An electric utilities stock that insiders are snapping up a large amount of stock in here is Dominion Resources  (D - Get Report), which produces and transports energy in the U.S. Insiders are buying this stock into modest weakness, since shares have dropped by just 2.2% over the last three months.

Dominion Resources has a market cap of $41 billion and an enterprise value of $67 billion. This stock trades at a fair valuation, with trailing price-to-earnings of 31.6 and a forward price-to-earnings of 18.2. Its estimated growth rate for this year is 8.2%, and for next year it's pegged at 5.1%. This is not a cash-rich company, since the total cash position on its balance sheet is $331 million and its total debt is $26.16 billion. This stock currently sports a dividend yield of 3.6%.

A director just bought 30,000 shares, or above $2.21 million worth of stock, at $73.67 per share.

From a technical perspective, D is currently trending just above its 200-day moving average and well below its 50-day moving average, which is neutral trendwise. This stock has been downtrending for the last month, with shares moving lower from its high of $79.19 to its intraday low of $69.78 a share. During that downtrend, shares of D have been consistently making lower highs and lower lows, which is bearish technical price action. That said, shares of D have now started to find some buying interest right around its 200-day moving average.

If you're in the bull camp on D, then I would look for long-biased trades as long as this stock is trending above Tuesday's intraday low of $69.78 a share and then once it breaks out above some near-term overhead resistance levels at $72 to $73 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 2.80 million shares. If that breakout hits soon, then D will set up to re-test or possibly take out its next major overhead resistance levels $74.08 to its 50-day moving average of $75.63 a share. Any high-volume move above those levels will then give D a chance to trend back towards $78 to $79 a share.

Merge Healthcare

One technology stock that insiders are warming up to here is Merge Healthcare  (MRGE), which develops software solutions that facilitate the management of images to create an electronic health care experience for patients and physicians worldwide. Insiders are buying this stock into major strength, since shares exploded to the upside by 74% over the last six months.

Merge Healthcare has a market cap of $433 million and an enterprise value of $585 million. This stock trades at a reasonable valuation, with a forward price-to-earnings of 17.2. Its estimated growth rate for this year is 5%, and for next year it's pegged at 23.8%. This is not a cash-rich company, since the total cash position on its balance sheet is $42.32 million and its total debt is $225.43 million.

An officer just bought 95,000 shares, or about $370,000 worth of stock, at $3.90 per share.

From a technical perspective, MRGE is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending very strong over the last five months, with shares moving higher from its low of $2.04 to its recent high of $4.73 a share. During that uptrend, shares of MRGE have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed shares of MRGE within range of triggering a near-term breakout trade.

If you're bullish on MRGE, then I would look for long-biased trades as long as this stock is trending above its 50-day moving average of $3.95 and then once it breaks out above some near-term overhead resistance at $4.60 to its 52-week high of $4.73 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 664,755 shares. If that breakout materializes soon, then MRGE will set up to enter new 52-week-high territory, which is bullish technical price action. Some possible upside targets off that move are $5.50 to $6, or even $6.50 a share.

Sprint

A wireless communications stock that insiders are active in here is Sprint  (S - Get Report), which provides wireless and wireline communications services to consumers, businesses, and government users in the U.S., Puerto Rico and the U.S. Virgin Islands. Insiders are buying this stock into decent strength, since shares have trended up by 11.7% over the last three months.

Sprint has a market cap of $20 billion and an enterprise value of $48 billion. This stock trades at a reasonable valuation, with a price-to-sales of 0.57 and a price-to-book of 0.91. This is not a cash-rich company, since the total cash position on its balance sheet is $3.71 billion and its total debt is $32.46 billion.

The CEO just bought 5.08 million shares, or about $25 million worth of stock, at $4.92 to $4.94 per share.

From a technical perspective, S is currently trending above its 50-day moving average and below its 200-day moving average, which is neutral trendwise. This stock has been uptrending over the last three months, with shares moving higher from its low of $3.79 to its recent high of $5.28 a share. During that uptrend, shares of S have been consistently making higher lows and higher highs, which is bullish technical price action. That move has now pushed shares of S within range of triggering a major breakout trade above some key overhead resistance levels.

If you're bullish on S, then I would look for long-biased trades as long as this stock is trending above some near-term support at $4.43 a share and then once it breaks out above some near-term overhead resistance levels at $5.28 to right around its gap-down-day high from last November at $5.50 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 19.55 million shares. If that breakout gets set off soon, then S will set up to re-fill its previous gap-down-day zone that started near $6.25 a share.

Bank of New York Melon

One final stock with some monster insider buying is Bank of New York Mellon  (BK - Get Report), which provides various financial products and services in the U.S. and internationally. Insiders are buying this stock into modest weakness, since shares have fallen by 1.8% over the last three months.

Bank of New York Mellon has a market cap of $44 billion and an enterprise value of $57 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 18.4 and a forward price-to-earnings of 12.7. Its estimated growth rate for this year is 8.8%, and for next year it's pegged at 19.2%. This is a cash-rich company, since the total cash position on its balance sheet is $162.86 billion and its total debt is $60.92 billion. This stock currently sports a dividend yield of 1.7%.

A director just bought 784,769 shares, or about $31.22 million worth of stock, at $39.78 per share. From a technical perspective, BK is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending over the last month, with shares moving higher from its low of $35.46 to its recent high of $40.03 a share. During that uptrend, shares of BK have been consistently making higher lows and higher highs, which is bullish technical price action. That move has now pushed shares of BK within range of triggering a near-term breakout trade.

If you're bullish on BK, then I would look for long-biased trades as long as this stock is trending above its 200-day moving average of $37.99 a share and then once it breaks out above some near-term overhead resistance at $40.03 a share with high volume. Look for a sustained move or close above that level with volume that hits near or above its three-month average volume of 5.52 million shares. If that breakout kicks off soon, then BK will set up to re-test or possibly take out its next major overhead resistance levels at its 52-week high of $41.79 a share. Any high-volume move above that level will then give BK a chance to trend towards $45 a share.

-- Written by Roberto Pedone in Delafield, Wis.

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