For a particular company’s market share and/or ranking in its industry, there are a number of options. As noted above, Mergent Intellect [Hoover’s/D&B] will sometimes provide market share in its profile of a company. The Standard & Poor’s Industry Surveys in S&P’s NetAdvantage are a second option, IBISWorld is very good and detailed for U.S. markets, and Euromonitor’s Research Monitor provide additional data for the consumer industries it covers. For NetAdvantage, one has to study the report detail, but usually the “Industry Profile” section will contain the relevant data if available. Quite often, rankings by sales are more commonly provided than a strict percentage market share. Or there might be a ranking on some other basis, like tonnage output in the steel industry. You also may be dealing with a firm that is highly diversified in its lines of business or products, in which case you’ll have to look at rankings or market share for particular business segments. Some industries themselves, like apparel retailers or restaurants, are extremely segmented, and this fact often makes the “market share” question much more elusive, or expensive!
A pretty good rule of thumb is that if one does not find the figure pretty quickly in such places as Mergent Intellect, S&P’s Industry Surveys, IBISWorld, or Research Monitor, it may be tough to get this figure short of your personally buying very expensive market research reports, which are obviously not going to be an option in the educational setting. These research reports can run into the thousands of dollars.