Boeing is predicting that the world’s airlines will buy 34,000 new airplanes over the next 20 years, driven by strong growth in China, India, and other emerging markets. That growth would double the size of the world’s airline fleet, Boeing said.

The airplane maker and defense contractor predicted that $4.5 trillion worth of planes will be sold. It will have to compete with Airbus and other competitors including Bombardier, Embraer, and China’s state-owned COMAC.

Boeing said the Asia Pacific region will be the biggest market for new planes, with a potential for 12,030 new planes there through 2031. The next biggest market is Europe with 7,760, and North America with 7,290.

Boeing said low-cost airlines are stimulating demand for air travel. Those airlines have been especially important in Asia, because they’re making air travel affordable for people who previously didn’t fly. Boeing predicted that airline traffic will grow 5 percent a year for the next two decades.

Boeing predicted that more than 23,000 of the 34,000 planes that will be sold will be single-aisle planes such as its 737 and the competing Airbus A320. It also predicted sales of 7,950 larger planes such as its new 787. Sales of each would total around $2 billion, because the bigger planes cost more.

The Chicago company reduced its projection for the number of freighter airplanes that will be sold. It says the cargo market remains sluggish. It predicted 940 new freighters would be needed, and another 1,820 passenger planes would be converted to haul freight.

Boeing does a detailed annual study of airline sales trends. Airlines order planes years in advance, so Boeing has to make production decisions years in advance, too.

Shares of Chicago-based Boeing Co. rose 62 cents to $73.80 in morning trading. They are trading near the high end of their 52-week range of $56.01 to $77.83.