Companies are having a hard time hiring for some positions despite growing unemployment, said Melanie Holmes, a vice president with staffing company Manpower Inc., which surveyed employers on hard-to-fill jobs.

A combination of factors are to blame. Some industries such as health care face surging demand. In other fields, such as engineering, new “green” energy initiatives are expanding opportunities. Engineering companies are having a hard time replacing retirees.

The list of positions employers said they had the most difficulty finding someone for included: Engineers, nurses, skilled/manual trades workers, teachers, sales representatives, technicians, short-haul drivers, information technology staff, laborers and machinists/machine operators.