Wal-Mart Stores (NYSE: WMT) is the world’s largest publicly traded employer, with approximately 2.2 million employees across of the globe, a number greater than the population of cities such as Houston, Philadelphia, and Phoenix.

In all, nearly 100 publicly-traded companies worldwide employ at least 175,000 workers each. These companies operate in a variety of industries, from fast food to energy to finance. They are also based throughout the world, from the United States to China to Russia to Germany. Based on figures from S&P Capital IQ, these are the largest employers in the world.

Employee count is just one indicator of a company’s size. The companies that employ the most workers are also extremely large by revenue. Of the top 15 global employers, five had revenues above $100 billion in their most recent fiscal year. Among these were Volkswagen, PetroChina (NYSE: PTR), and Wal-Mart Stores, which had more than a quarter of a trillion dollars in revenue each.

Many of the largest publicly traded employers are in labor intensive sectors, relying more on their employees to drive the business than on such factors as technology and equipment. For instance, G4S and ISS are support service companies that outsource workers to various companies and institutions. These organizations rely on such workers to provide cleaning, security, and other services. Other companies, such as retailers and restaurants, rely on a large staff to run their stores. Wal-Mart Stores and McDonald’s (NYSE: MCD) are examples of such companies.

Many of these companies have become large employers because they were once key government agencies. For example, the now private Deutsche Post was once the German government’s postal service. Russia’s Gazprom, as well as Industrial Commercial Bank of China and Agricultural Bank of China were also entirely government-owned until recently. The Russian government remains the majority owner of Gazprom. Chinese state-owned agencies still held majority stakes in ABC and ICBC, as well as oil and gas giant PetroChina, as of the end of last year.

Many of these companies benefit from their location. Notably, three of the largest employers are based in China. The world’s second largest economy has a total population of over 1.3 billion people, the most of any country in the world. Another three companies, including IBM (NYSE: IBM), McDonalds, and Wal-Mart Stores, are based in the U.S., also one of the world’s most populous countries and the largest by GDP.

Many of these companies benefit from a truly dominant presence in their home market. The majority of Wal-Mart Stores’ 2.2 million employees are based in the U.S. Similarly, the majority of global service provider ISS’s business is located in Western Europe, where the company has more than 200,000 employees and generates 51% of its revenue.

Other top employers have a large global presence. Sodexo maintains operations in 80 countries. For companies like ISS and G4S, recent emerging market growth has driven revenue growth and increased headcount. A large global presence, especially in industries such as food, cleaning, and security, allows a company to provide easy outsourcing options for local employers.

To determine the 15 publicly traded companies with the most employees worldwide, 24/7 Wall St. used figures from S&P Capital IQ. We then independently verified employee totals from each of the top 15 companies. When companies distinguished between part-time and full-time employees in their financial statements, S&P Capital IQ calculated part-time employees as half of a “full-time equivalent” worker. When companies did not distinguish between part-time and full-time workers, all employees were treated as full-time by Capital IQ. Capital IQ converted revenue figures of foreign companies into dollars based on the date at the end of each company’s filings.

These are the biggest employers in the world.