Engineers rank as the hardest jobs to fill, according to a list of the 10 hardest jobs to fill by Manpower Inc. (NYSE: MAN). Sales representatives had topped last year's list, but slipped to No. 5 this year.

After engineers, the other top 10 hardest-to-fill jobs this year, in order, are machinists/machine operators, skilled trades, technicians, sales representatives, accounting and finance staff, mechanics, laborers, information technology staff, and production operators.

The results come from a Manpower global study conducted in January of more than 42,500 employers in 32 countries and territories.