The first generation 737s (737-100s and 737-200s) were first ordered in 1965 and were delivered in December of 1967. Since that time, Boeing has continually modified its smallest line of jets, resulting in the current generation of 737s, which includes the enlarged 737-300 (first delivered in 1984 to USAir), the further enlarged 737-400 (first delivered in 1988 to Piedmont Airlines), and the smaller 737-500 (first delivered in 1990). Today Boeing is in the process of producing the next-generation of 737s, comprised of the 600, 700, and 800 series, the first of which are scheduled for delivery in October 1997. Changes include a larger wing, higher cruise speed, increased range, and new engines with improvements in noise, fuel burn and thrust. With over 3,300 orders the Boeing 737 has become the world's all time best-selling commercial jetliner. Over 2,700 have already been delivered to more than 250 customers in 95 countries. By 1996, 737s had carried more than 4.3 billion passengers and flown more than 26.6 billion miles. Through March 31, 1996, the current generation 737 was the most reliable jet airplane in commercial aviation, with a dispatch reliability of 99.4%. Over 700 737s are in the sky at all times.