The Delaware North Cos., a hospitality company whose customer-service representatives help people plan vacations at national parks, sometimes struggles these days to keep 80 or so seats filled at its call center in Fresno, Calif.—a city tied for the 9th-highest unemployment rate in the U.S.

The company has no shortage of job applicants. But finding the right candidates has gotten tougher since the company started using a customized assessment last year to see how applicants stack up against top call-center workers in such traits as friendliness, curiosity and the ability to multitask.

Managers said the new test, administered online, has reduced turnover and allowed Delaware North to more accurately select applicants who best fit the job. “Now we understand better what makes a great reservation sales applicant,” said Andy Grinsfelder, vice president of sales and marketing for the Buffalo, N.Y.-based company’s parks and resorts division.

Pre-hire assessments have been used for years, but never have such tests been deployed so widely at companies across the U.S. The automation of the job application process, combined with powerful data tools and inexpensive online software, have led to falling costs, more accurate results and a surge in use.

Eight of the top 10 U.S. private employers now administer pre-hire tests in their job applications for some positions.