Part-time firefighters were unavailable a third of the time at one station in Nottinghamshire during a three-month period.
Figures show a mixed picture across the county – with some stations having on-call fire crews available 97 percent of the time in the last three months of last year.
However at six stations, on-call fire crews are available less than 80 percent of the time.
The fire service says it has plans in place to improve performance, including an ongoing recruitment drive.
Despite the relatively low figures in some areas, all stations but one have increased their on-call availability from the previous period.
Southwell fire station had the worst performance, with the crew unavailable for 735.5 hours over the three months.
When no on-call crew is available, the fire service will send the nearest available engine, however this can result in delays.
In the busiest areas, fire stations are manned 24 hours a day, while quieter stations are covered by on-call crews.
It comes after Nottinghamshire Fire and Rescue Service announced that two stations – Ashfield and Retford – would move from being full time stations to being a hybrid of full-time and part-time, known as ‘mixed crewing’.
The decision – which proved controversial with groups including the Ashfield Independent party – was made to save the service £500,000 per station.
In Retford, the on-call crew was available 77.7 percent of the time, while the Ashfield crew was available 94.8 percent of the time, over the three-month period.
Wayne Bowcock is the deputy chief fire officer, and said: “We’ve been focussing on improving the availability of our on-call fire appliances for more than two years.
“We’ve been working with the National Fire Chiefs Council and learning from other areas, sharing good practice.
“We’re investing time and effort with our on-call managers to understand their local issues and work with them to make sure we can give them the most support we can.
“We want to help our firefighters give as much cover as possible while they juggle busy personal lives and other employment.
“We recognise the huge contribution our on-call fire fighters make to community safety across Nottinghamshire."