In a victory for common sense, the trading behavior of company executives, directors, and large shareholders in the stocks of firms they're registered "insiders" at have been proven profitable to monitor by both academic studies and (more importantly) the experience of your fellow professional investors.

Below are lists of the top 10 mainly open-market insider purchases and sales filed at the Securities and Exchange Commission Thursday, January 31, 2013 as ranked by dollar value.

Please note, however, that these are factual lists, not buy and sell recommendations. Dollar value is only one metric to assess the importance of an insider transaction, and, frankly, often not even the most important metric that determines if an insider transaction is significant.

In purchases, Molibdenos y Metales S.A., the world's largest processor of molybdenum and rhenium, bought $90 million worth of stock in Molycorp (NYSE:MCP), which makes and sells rare earth oxides. Molycorp announced today that Molibdenos y Metales would be investing approximately $390 million in the rare metals company, in exchange for 12.5 million shares. The data storage products and services corporation EMC (NYSE:EMC) bought $19,983,032 worth of stock in cloud infrastructure and virtualization company VMware (NYSE:VMW). Investment firm Three Arch Capital, a beneficial owner of LipoScience (NASDAQ:LPDX), the in vitro diagnostic company that develops and markets diagnostic tests, bought $1.935 million worth of company stock.

In sales, Eric Schmidt, Chairman of Google (NASDAQ:GOOG), sold $53,579,719 worth of company stock. At wireless telecommunications company MetroPCS Communications (NYSE:PCS), CEO Roger Linquist sold $1,731,252 worth of stock. Peter Mosling Jr., a Director of specialty vehicle company Oshkosh Corporation (NYSE:OSK), sold $1.582 million worth of company stock. Peter Ricketts, a Director of TD Ameritrade (NYSE:AMTD), sold $893,640 worth of company stock. Bradley Rencher, Senior Vice President and General Manager of software company Adobe (NASDAQ:ADBE), sold $801,326 worth of company stock.

At InsiderInsights.com, we find new investment ideas just about every day using these and more intricate insider screens to determine where we should focus our subsequent fundamental and technical analysis. And while stocks don't (or shouldn't) move up or down based on insider activity alone, insiders tend to be good indicators of when real stock-moving events like earnings surprises, corporate actions, and new products may be in the offing.

Insider Purchases

#:	Filer Name	Insider Titles	Company Name	Ticker	Trans Type	Dollar Value
1	Molibdenos Y Metales	BO	Molycorp	MCP	JB*	$90,000,000
2	EMC	BO	VMware	VMW	B	$19,983,032
3	Three Arch Capital	BO	Liposcience	LPDX	JB*	$1,935,000
4	Pennant Capital Mgt	BO	Universal Stainless	USAP	B	$217,630
5	Simmons Harold C	CB,DIR,BO	Valhi	VHI	B	$156,005
6	Erickson Ronald P	CEO,DIR	Visualant	VSUL	B	$136,290
7	Gambill Mark M	DIR	Newmarket	NEU	B	$128,035
8	Johnson Warren C	VP	Moog	MOGA	JB*	$102,971
9	Pepper Jon	DIR	Visualant	VSUL	B	$82,500
10	Brugger Thomas R	VP,CFO	Sun Bancorp	SNBC	B	$68,619

Source: InsiderInsights.com | Key to Insider Title and Trans Type Codes
 

Insider Sales

#:	Filer Name	Insider Titles	Company Name	Ticker	Trans Type	Dollar Value
1	Schmidt Eric E	CB,DIR	Google	GOOG	AS	$53,579,719
2	Addington Hills	BO	Ixia	XXIA	S	$2,237,058
3	Linquist Roger D	CEO,DIR	MetroPCS Comms	PCS	AS	$1,731,252
4	Mosling J Peter Jr	DIR	Oshkosh	OSK	S	$1,582,000
5	Schulte Daniel C	VP,GC	Waddell & Reed Finl	WDR	S	$1,063,839
6	Credit Suisse Ag	BO	Walker & Dunlop	WD	AS	$990,781
7	Ricketts J Peter	DIR	Td Ameritrade	AMTD	S	$893,640
8	Rencher Bradley	VP,SO	Adobe Systems	ADBE	S	$801,326
9	Erdoes Mary E	MD	JPMorgan Chase	JPM	S	$705,300
10	Sarver Robert G	CB,CEO,DIR	West Alliance Banc	WAL	S	$660,857

Source: InsiderInsights.com | Key to Insider Title and Trans Type Codes

Editor's note: Jonathan Moreland is the founder of Insider Insights and author of "Profit From Legal Insider Trading."