Wireless and fixed network speeds in the U.S. have been steadily increasing, although the nation still lags behind many other countries, according to the latest Speedtest data from the Internet diagnostics firm Ookla.

The company's report for the first and second quarters of this year also shows that T-Mobile is currently in first place for average mobile network speeds in the U.S., easily beating the traditional leaders Verizon and AT&T and far ahead of Sprint.

Those results, however, are not as surprising as they initially seem. Tests last month by the wireless coverage mapping company OpenSignal also found T-Mobile's network speeds in the lead, due in part to Verizon's and AT&T's revival of unlimited data offerings earlier this year.

'First All-LTE Mobile Carrier'?

Ookla uses its Speedtest technology to measure upload and download speeds for wireless carriers nationwide. The company then calculates a speed score for each service provider based on performance across the carrier's entire network, with 90 percent of the score based on download speeds and 10 percent based on upload speeds.

"T-Mobile has the fastest mobile network in the United States, clocking in with a Speed Score of 23.17 on modern devices during Q1-Q2 2017," according to the Speedtest results published today. "The combination of a tightly-spaced cell site grid and a smaller subscriber base than Verizon and AT&T could be the keys to T-Mobile's success in the U.S. market and to their ability to support the exponential growth in mobile data consumption."

Another likely factor in T-Mobile's improvement is its aggressive strategy to expand its 4G LTE coverage, the Speedtest report noted. In addition to its recent efforts to expand its LTE footprint in the 700 MHz spectrum space, T-Mobile is also rapidly deploying a 600 MHz LTE network using nearly $8 billion in low-band spectrum the company purchased from the Federal Communications Commission earlier this year.

"T-Mobile is in an excellent position to become the first all-LTE mobile carrier in the United States which will allow them to deliver voice and data more efficiently," according to the Speedtest report, which added that the company's advanced LTE features also include Wi-Fi calling, HD voice services, and LTE in the unlicensed 5 GHz band.

Xfinity at the Lead in Fixed Broadband Speeds

Second-place Verizon, which earned a speed score of 21.13, "delivers consistent and reliable performance across its large footprint, while AT&T, one of the first carriers to adopt LTE in the U.S., had a speed score of 20.05, the Speedtest report noted. Despite a "notable drop in performance" with its new and expanded unlimited plans, AT&T has begun bouncing back in recent months due to a combination of new LTE deployment, supplemental downlink, and spectrum refarming efforts, and "still has a lot of room for incremental capacity gain," according to the Speedtest report.

Sprint's Speed Score of 15.39 put it in fourth place, although the company has made "significant improvements" since last year and is well-positioned for further gains, the report noted.

Overall, Ookla found that average mobile download speeds in the U.S. now stand at 22.69 Mbps, an improvement of 19.2 percent compared to the first and second quarters of 2016. That places it behind 43 other countries, with Fiji and Germany ahead of the U.S. and Oman just behind.

The U.S. performs better in terms of fixed broadband speeds, Ookla added. With an average national download speed of 64.17 Mbps on fixed networks, the U.S. ranks 15th globally, behind the Netherlands and just ahead of Spain. The U.S. carrier with the fastest fixed-network speed score was Xfinity (69.58), followed by Verizon Fios (66.74), Cox (64.85), Spectrum (51.45), AT&T Internet (49.59), Frontier (31.70), and CenturyLink (14.91).