Harry Roberts and Al Purcell are vying for the nomination.
Between the two, they've raised $75,000.
According to the most recent campaign reports filed, Roberts has raised $42,851 and spent $17,352 so far.
Purcell has raised $32,390 and has spent $9,364 to this point.
The winner of the Republican primary will face Democrat Mike Veale, who is running unopposed for his party's nomination.
Current Presiding Commissioner R.T. Turner is stepping down after two terms in office.