Oregon voters appear on track to show their lowest turnout in a primary election in at least 16 years, ballot statistics indicate.

As of 9 a.m. Monday, about 19 percent had turned in their ballots, compared with the previous low of 25 percent the Monday before the 2014 primary.

Total turnout in May 2014, Oregon's most recent non-presidential nominating election, reached just 35.5 percent.

The count of registered Oregon voters has increased each year, driven in large part by the Oregon Motor Voter law. That form of automatic voter registration took effect in January 2016 and prompted a 14 percent jump in voter registration, which may play a part in this year's lower percentage turnout.

The number of total ballots received as of Monday morning before the election is lower as well -- 495,987 compared to 527,139 in 2014.

But that may be due in part to an anomalously low count of ballots returned Friday and over the weekend and tallied by the state elections office Monday morning.

This year's count of ballots returned on Friday and over weekend was 12,527 ballots, compared to 97,200 ballots in 2014, 95,730 in 2010 and 80,879 ballots in 2006.

Debra Royal, chief of staff to the Oregon secretary of state, could not explain the discrepancy.

There are no high-profile, high-spending statewide primary contests this year. Gov. Kate Brown is expected to easily win her party's nomination, and all five members of the U.S. House of Representatives are considered shoo-ins for new terms.

In the race for Labor Commissioner, the two leading contenders have raised about $1.1 million, with Democrat Val Hoyle garnering more than twice as much campaign cash as her opponent, Republican Lou Odgen.

In Multnomah County, with the state's highest voter registration, elections office spokesman Eric Sample said that voter turnout seems to be higher than in previous years. By end of day Monday, 95,276 Multnomah voters had returned their ballots, compared to 84,801 in 2014.

Ballots are due by 8 p.m. Tuesday.

-- Corlyn Voorhees