Despite major network investments, U.S. wireless carriers are at the back of the pack when it comes to delivering a quality app experience for customers.

According to a new study from STL Partners that quantitatively measured customer app experience, all four tier-1 U.S. carriers ranked in the bottom half of operators among their global peers in the fourth quarter 2015.

STL called the results a “raw deal” for U.S. consumers given the relatively high prices they pay for mobile broadband.

The report, completed in collaboration with Apteligent, assigned operators an individual Mobile Network Customer Experience Index, or MobiNEX, score based on their performance across four measures: download speed, average latency, error rate and latency consistency. Scores for each measure were given on a 25-point scale, with total scores ranking on a 100-point scale.

The top performers in the report – Bouygues Telecom, Free and Orange – were all French operators with scores of 70 or above. The lowest scoring operators in the report were Germany’s E-Plus and Italy’s Wind, each with a score of 26.

The top ranked U.S. carrier was T-Mobile, whose overall score of 45 was 31 points below Bouygues’ high score and 4 points below the median operator score. T-Mobile garnered middling marks for latency consistency (13/25), download speed (12/25) and average latency (14/25), but received poor marks (5/25) in the error rate category.

Verizon’s performance put it on T-Mobile’s heels with an overall score of 43. The carrier trailed T-Mobile by at least one point in error rate, latency consistency and average latency, but pulled ahead by one point in the download speed category. Verizon received the lowest score (4/25) among U.S. carriers in the error rate measure.

AT&T trailed both Verizon and T-Mobile with a total score of 37, earning the best error rate marks (6/25) out of the U.S. carriers but also the worst scores in latency consistency (10/25).

In last place among U.S. operators and in the bottom five overall was Sprint, with a total score of 33. Sprint’s highest rated measure of performance was average latency, where it tied Verizon with a score of 13 out of 25.

The poor error rate performance across the board in the United States stood out to STL researchers.

“All the U.S. operators perform poorly on error rate,” STL wrote in its report. “This is a real surprise given that many applications have been developed in the U.S.-based start-ups and established companies and the vast majority are hosted in the data centers of U.S. internet giants – Amazon and Google being particularly important.”

According to STL, the importance of the app experience report is that it reflects the actual experience of customers when they use applications on different mobile networks. The measurements, STL said, “allows individual operators to see how they are performing in relation to the competition in an objective and quantitative manner.”

STL said it has also found a strong positive correlation between its MobiNEX scores and customer satisfaction measurements taken by the American Customer Satisfaction Index and the United Kingdom’s National Customer Satisfaction Index.