The number of passengers using Ontario International Airport in 2009 was at its lowest level since 1988, a decade before two twin terminals that could hold 10 million passengers were built, according to airport statistics released Tuesday.

The airport had 4.88 million travelers fly in and out in 2009, 21.6 percent fewer than in 2008.

A forecast from Los Angeles World Airports, the LA city agency and airport’s owner, released last year predicted that 4.83 million passengers would use Ontario airport before the end of 2009.

At Los Angeles International Airport, also owned by LAWA, the number of passengers declined 5.6 percent in 2009 compared with the year prior to 56.5 million passengers.