Research shows that Glasgow was the only city to record an increase in occupancy; averaging 87.4% when compared with Edinburgh and Aberdeen.
The figures reflect a 9.5% rise compared with May 2013.
May was the 12th consecutive month of record-breaking year-on-year occupancy rates for Glasgow's hotels.
Meanwhile, occupancy in both Edinburgh and Aberdeen fell by 3.4% and 3.8% to 88% and 76.5% respectively.
Specifically, on 13 nights last month, occupancy reached 95% or more; peaking at 99% on May 20, which coincided with US-band Nine Inch Nails performing at the SSE Hydro and again on May 24, which was BBC Radio 1's Big Weekend at Glasgow Green.
The research was carried out by tourism market research specialists LJ Research.