Looking to become a tucker? There are tons of carrier companies out there to work for, but most likely, you'll be working for one of the really big companies that represent the backbone of the U.S. trucking industry. To familiarize yourself with the business, here are the top five largest carriers in the U.S. as of 2003.

1. United Parcel Service - You may know them best as UPS or, as "The Brown Machine." UPS is headquartered in Sandy Springs, Georgia and UPS delivers more than 15 million packages a day to 6.1 million customers in more than 200 countries and territories around the world. Ironically, this massive company was started in 1907 by two teenagers as the American Messenger Company. They capitalized the start-up with a $100 loan and grew it into a multi-billion dollar company.

2. FedEx Ground - This shipping juggernaut was created to take advantage of new bar code, material handling and computer technologies and has expanded to cover the entire United States. As of 2009, FedEx ground employs over 70,000 people.

3. Schneider National - It is the largest privately-owned truckload carrier in the United States and is headquartered in Green Bay, Wisconsin. Schneider National operates 14,000 tractors, 40,000 trailers, and has partnerships with over 6,000 carriers. Schneider drives more than five million loaded miles per day, and provides services to more than two-thirds of the companies in the Fortune 500.

4. Roadway - Through its full-service network, consisting of 349 service centers, and with its 32,119 trailers and 8,426 tractors, Roadway is able to deliver over 49,000 shipments per day. Roadway employs over 23,000 people and their trucks are easily recognizable by their ROADWAY logo that is printed boldly across their trailers.

5. Yellow Transportation Inc. - Originally founded as the Yellow Cab and Transit Company, a bus and taxi company that served central Oklahoma. Why are Yellow's vehicles actually orange, you may ask? Because in 1929, a study was done for safety concerns which determined that the color of the swamp holly berry would be most visible from the greatest distance. Swamp Holly Orange became the color used on all company tractors.

If you're looking for employment after graduating from a trucking school, going to work for a major carrier just may be in your best interests. The economic conditions after the 2008 financial meltdown have put many companies in on a not-so-great footing, so getting in with one of the larger, more sustainable companies may be the best idea for someone just starting their career. The good news is that after graduating and getting your CDL license, you can enter the lucrative world of driving an 18-wheeler. But be careful not to rush into working for a company until you've thoroughly gone over your employment options.