More than a third of hiring managers currently have positions that have remained open for 12 weeks or longer, according to new research by the online lob listing service CareerBuilder. Among the hardest to fill are slots for truck drivers.

“Two in five employers reported that they continuously recruit throughout the year, so that they have candidates in their pipeline in case a position opens up down the road,” says Brent Rasmussen, president of CareerBuilder North America.

CareerBuilder found since 2010 there have been 113,517 new jobs for truck drivers created in the United States, translating into a growth rate of 6.7% and the fourth highest on its list of the jobs most difficult to fill.

Among the jobs that were cited as most difficult to fill, in order of jobs added are:

• Sales Representative, 584,792 new jobs added from 2010 to 2013, 3.8% job growth from 2010 to 2013

• Machine Operator/Assembler/Production Worker, 135,363 new jobs, 9.9% growth

• Nurse, 135,325 new jobs, 5% growth

• Truck Driver, 113,517 new jobs, 6.7% growth

• Software Developer, 103,708 new jobs, 11.2% growth

• Engineer, 73,995 new jobs, 4.9% growth

• Marketing Professional, 57,045 new jobs, 11.3% growth

• Accountant, 55,670 new jobs, 4.5% growth

• Mechanic, 53,002 new jobs, 4.1% growth

• IT Manager/Network Administrator, 48,709 new jobs, 7.5% growth