There are many sources of information that Warren uses to assist with his investment decisions. In print, Warren reads the Wall Street Journal, New York Times and Washington Post daily along with other regional newspapers along with magazines such as Fortune, Forbes and Business Week.
The internet also provides many useful sources of information which Warren utilizes. Online, Warren uses Value Line Investment surveys, Moody's Stock Guides, Standard and Poor's Stock Reports, SEC EDGAR Database, Bloomberg's and PRNewswire. Local libraries often have access to reports from these informational service companies and is an alternative way of getting access to the reports these companies produce.
Warren only invests in companies which he understands and thus fall within his circle of competence. Sometimes, Warren needs to increase his knowledge about a particular business in order to determine if a competitive durable advantage really exists. To learn more about a busines, Warren often uses a technique called the "scuttlebutt" method of investigating potential investments. This scuttlebutt method involves calling around to competitors and various persons involved in the business in order to increase his knowledge of the situation.
The methods which Warren uses to gain knowledge in order to make investment decisions are widely available.