Most company rankings are based on financial factors, either the volume of sales or revenue generated. It is expressed as the percentage of total sales of a given market held by each competitor. An important consideration is how broadly or narrowly the particular market is defined. The significance of a company's market share depends entirely on the market being measured. Finding information on market share can sometimes be difficult.
Trade journals are often the best source to check.
Use the periodical indexes to look for relevant data. Then, scan standard industry sources. There are two major sources of company or market rankings. The business press is one source and industry associations are another. To retrieve rankings from these producers, you will need to use the business indexes.