Southwest ranked first among North American carriers in on-time performance (OTP) in January, according to the latest report from Cirium, an aviation data provider. Delta Air Lines had the best OTP for 15 of the last 16 months prior to January. Southwest’s OTP for the month was 83.3%, an improvement of 4.3 percentage points over December.

Delta’s OTP was 81.1% in January, putting it in fourth place behind Alaska Airlines (82.6%) and Spirit Airlines (81.1%). (Spirit beat out Delta by 0.07 percentage points.)

Overall, North American OTP improved over December’s figure, with an average of 77.9%, up from the 74.8% reported last month. All but one carrier had an improved month-over-month score. Frontier Airlines’ average dropped 2.4 percentage points to 73.1%, but it still came in ahead of WestJet and Air Canada, even though those carriers’ figures improved 5.6 percentage points and 6 percentage points, respectively, month over month.

Delta was the only North American airline to reach the top performing global airlines list, ranking ninth.

Spirit was the only carrier with a January completion factor of 99% or better. Alaska was second at 98.9%, followed by Southwest and Delta at 97.4% and United Airlines at 97.2%.

The number of January flight cancellations increased to 20,885, up from the 7,045 reported in December.