What is 'Market Share'?
Market share represents the percentage of an industry, or market's total sales, that is earned by a particular company over a specified time period. Market share is calculated by taking the company's sales over the period and dividing it by the total sales of the industry over the same period. This metric is used to give a general idea of the size of a company in relation to its market and its competitors. Market Share Definition from Investopedia
Market share information can be found in news articles about a company in trade journals for an industry, in industry reports, and in some of these sources listed below:
Market Share Reporter in Gale Business Essentials database. Link from NYPL catalog. Note: In the Business Insights Essentials database, from the main search screen, just mouse over the "Industries Tab" and select "Market Share". On next screen search for an industry (or company) and limit results by latest year or range of dates.