The Trucking Industry is a cyclical sector comprised of companies that provide shipping services, using tractor-trailers, to customers, which are usually commercial businesses. Most trucking outfits own and operate the vehicles in their fleets, though some do rely on leasing. The vast majority of revenue is generated domestically, since overseas shipments require either air- or sea-based transportation. Thus, these companies have little exposure to foreign currency fluctuations. The industry tends to be a leading indicator for the overall economy. During the early stages of an economic upswing, customers begin to ship more goods in anticipation of stronger business conditions. Conversely, a decrease in trucking demand may signal the beginning of an economic slump.