Some databases can create competitor lists and others will have articles that can be searched for this information. Sometimes companies that appear similar may show up in different industries, so be sure to look in related industries for direct and indirect competitors. Indirect competitors can often be found in market research and industry reports. Keep in mind that there may not be industry classification connections for company subsidiaries and smaller divisions.
The databases below can be used to find market share information. It can be found in tables or within news reports and articles. Try searching the company or product name with the term "market share" or "brand share" or "market size", etc. Example: Costco AND "market share"