May Class 8 truck sales in the United States were up 1.3 percent over April, according to WardsAuto.
Wards said 19,195 Class 8 units were sold in May compared with 18,950 in April.
Mack and Volvo nameplates show the biggest month-over-month increases at 36 percent and 30.5 percent, respectively.
While sales were only slightly up in May compared to April, year-to-date sales continue to show significant improvement.
Through May 2018, 88,674 Class 8 trucks have been sold in the United States, compared with 67,012 in the first five months of 2017, a 32.3 percent increase.
International has posted the biggest year-over-year gain at 66.5 percent followed by Volvo at 53.7 percent.
Freightliner was the market share leader in May at 31.5 percent.