Mobile networks in the United States are faster than they’ve ever been, but Verizon’s is still the speediest, according to the latest study from PCMag.com.

And Sprint’s is least consistent, the media outlet said.

PCMag.com tested data speeds of the four major carriers in 30 U.S. cities using Samsung Galaxy S8 phones running a customized version of Ookla’s Speedtest.net application. More than 124,000 data points were collected in categories such as downloads, uploads, latency and reliability.

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Verizon earned an overall score of 97, edging out T-Mobile’s 96, and AT&T scored 93 points. Sprint finished a distant fourth with 74 points.

American operators have consistently seen their network speeds improve since PCMag issued its first study in 2010. Data speeds roughly double every two years, Sascha Segan of PCMag.com wrote, jumping from 50-60 Mbps in 2014 to 120 Mbps in 2016 and reaching 200 Mbps in the latest study.

PCMag’s analysis mirrors a similar study from OpenSignal earlier this year. OpenSignal reported that Verizon’s average LTE download speed was 16.89 Mbps, essentially tying T-Mobile’s performance of 16.65 Mbps. AT&T’s network ranked third in LTE download speeds, OpenSignal said, and Sprint’s took fourth place.

But while OpenSignal’s study indicated that the “network gap” between all four major operators had narrowed significantly in recent years, PCMag reported that Sprint appears to have stumbled recently.

“Sprint seems to have hit a roadblock after vaulting hugely forward between 2015 and 2016,” Segan wrote. “While we saw the same spectacular peak speeds on Sprint that we got on the other carriers, they were far less consistent; Sprint's speeds would shoot up and then plummet within cities more often than other carriers, creating lower averages.”

The reasons for any “roadblock” aren’t clear, of course, and it’s unfair to draw any major conclusions from a single study. But Sprint consistently surprised analysts last year when it repeatedly lowered its guidance for capex on its network, which at times raised analysts’ eyebrows. Sprint has heavily marketed its network improvements over the last 18 months, and questions about the quality of its service could prove especially costly in a market that has grown extremely competitive.