Many aviation experts view U.S. airlines' growing use of small "regional jets" (RJ) as a revolutionary development that is significantly changing the aviation marketplace. The public tends to prefer travel by jet, and RJ (seats between 21 and 70 passengers) tend to have lower operating costs than larger "mainline" jets. This report examines how U.S. air carriers are using RJ and what issues surround the carriers' abilities to use these aircraft. It focuses on the following questions: what is the status of RJ deployment in the U.S., and how has this service evolved?; what factors have affected the airlines' decisions in deploying RJ?; and what effects have RJ had on air traffic and airport congestion. Illus.