Retail sales of U.S. and Canadian Class 8 Natural Gas trucks have increased in 2019, reversing the declining trend from the year before, according to ACT Research’s Alternative Fuels Quarterly.

As of May, year-to-date sales were up 43% and were also up 10% from April’s numbers.

“Bucking the early decline pattern of the past few years, cumulative sales for the first five months of 2019 appear to be gaining ground,” said Ken Vieth, senior partner and general manager at ACT Research. “Despite soft reports in three of the first five months this year, sales of natural gas-powered vehicles are on an overall upward trajectory, gaining 10% month-over-month, 60% compared to May of 2018, and showing 43% improvement against the first five months of last year.”

Refuse fleets were the biggest purchaser of new Class 8 natural gas trucks. Other big adopters were transit and school bus fleets.

In the trucking industry, the majority of new natural gas trucks were purchased by buyers that were replacing other natural gas trucks or increasing the size of their fleets.