The U.S. ranked dead last in a survey of 12 leading countries in average 5G mobile download speeds, according to research firm Opensignal.

U.S. phone users got an average 5G download speed of just 50.9 megabits per second, only about twice as fast as on older 4G LTE networks. At 50.9 Mbps, a user would need more than five minutes to download a typical high-definition movie.

In contrast, Saudi Arabian users had the fastest average 5G speed at 414.2 Mbps, or 14-times faster than average 4G download speeds in that country, Opensignal said. At that rate, an HD movie would download in 41 seconds.

Second place went to South Korea at 312.7 Mbps while Australia was third at 215.7 Mbps.

Wireless carriers worldwide are spending tens of billions of dollars to upgrade their networks to 5G, which ultimately should provide download speeds 10 to 100-times faster than the average 4G speed. But the technology suffers from glitches and is not widely deployed in all countries. The result is a highly uneven experience, even for customers who have upgraded to a 5G-capable phone.

The key reason that U.S. lacks speedier service is the type of the airwave bands that carriers are using for 5G. In most other countries, carriers use the 3.5GHz band, which provides a good balance of speed and availability, but that band has been unavailable to wireless carriers in the U.S.

In the U.S., AT&T and T-Mobile so far are building their 5G consumer networks for lower bands like 600MHz that provide wider coverage with much slower speeds. Verizon uses a much higher frequency, 28GHz, which provides extremely fast speeds but minimal coverage.

The situation in the U.S. should improve, as T-Mobile rolls out 5G in the 2.5GHz band. The federal government also plans to auction more spectrum in the 3GHz to 4GHz band soon, which the carriers will likely acquire to improve their 5G networks.

The different approaches by U.S,. carriers added a caveat in the speed measurements for the U.S., Opensignal noted. The rankings are based on an average that combined users of all three carriers. But looking at just Verizon’s faster 5G technology, Opensignal said the average U.S. download speed would reach 494.7 Mbps, higher than the average of any other carrier in any of the 12 countries.

The Opensignal rankings also measure how likely users were to find a 5G signal. That metric shows whether 5G coverage is spotty or widespread.

Users in Saudi Arabia, again, was tops with 34% availability. Meanwhile, the U.S. ranked fifth with 19% availability. T-Mobile and A&T’s slower 5G coverage is available in areas where about two-thirds of people in the country live, while Verizon’s speedy 5G is offered only in limited areas of a few dozen cities.

For its survey, Opensignal tracked average speeds by monitoring users of its mobile apps. The speed tests were conducted from May 16 to August 14.