The UK-based firm has also alleged 'discrepancy' in methodology used by the telecom regulator Trai compared to the method it uses to measure the speed.
"Airtel's average peak speed test was 56.6 Mbps, which is 5 times faster than its average 4G download test of 11.5 Mbps," A blog post on OpenSignal website said.
The test for the report was conducted between December 1, 2016 - Feb 28, 2017 in the metro cities of Delhi and Mumbai and the states of Karnataka and Tamil Nadu.
However, in the new parameter of average peak speed, it found Jio next only to Airtel.
More From This Section
"We measured Jio's average peak speed at 50 Mbps, which is nearly 13 times faster than its everyday 4G speed download speed of 3.9 Mbps," the blog said.
As per data published by the Telecom Regulatory Authority of India (Trai), Reliance Jio has been the fastest 4G service provider since the last seven months.
Trai collects data through its mobile application Trai MySpeed from users across the country on real-time basis. The users of the application can check the speed of their service provider anywhere and anytime and they have option to submit the test result to the regulator.
The firm said that it feels average peak speed is an accurate measure of a 4G connection under the most optimised conditions, and it gives an indication of what consumers might really experience when unfettered by congestion or technical limitations.
It said that Jio's networks are capable of supporting some incredibly fast LTE connections when conditions are ideal but as per the data that OpenSignal has "those ideal conditions were far more rare for Jio subscribers than for customers of other operators".
It said that Jio has added over 100 million customers in few months and has been offering them unlimited access to mobile data.
"That kind of heavy usage is bound to tax any network, forcing users to vie against one another for bandwidth. Our data shows that Jio's slow average 4G speeds aren't a technical limitation, but rather a capacity bottleneck," the blog said.
OpenSignal said that as Jio adds more capacity - either through new spectrum or building more cell sites - or if Jio's mobile data consumption levels drop then its typical download speeds should increase.