Voters in 36 out of 50 US states will elect their highest official, with the Democrats needing to gain only four states to tip the balance of power their way. The Republicans currently have 28 governors, the Democrats 22.
Governors' offices are regarded as important weapons for presidential candidates, helping to raise funds and delivering votes at election time.
The following are selected marquee gubernatorial races to be contested tomorrow:
Arkansas
Michael Beebe aims to be the first Democrat governor for over a decade but Republican rival Asa Hutchinson has narrowed the gap in recent polls.
California
Hollywood star Arnold Schwarzenegger is on course for a landslide Republican victory over Democrat candidate Phil Angelides.
Colorado
Democrat Bill Ritter is on course to beat rival Bob Beauprez in a seat left open by a Republican incumbent.
Florida
The key battleground in the 2000 election, the Republicans' Charlie Crist is a narrow favourite to edge out the Democrats' Jim Davis.
Idaho
Staunchly Republican for years -- all of Idaho's Congressional representatives are from the GOP -- Democrat challenger Jerry Brady has closed the gap on Republican rival Butch Otter.
Maryland
Republican incumbent Robert Ehrlich is neck-and-neck with Democrat Martin O'Malley in a race that is too close to call.
Massachusetts
Former Clinton administration justice official Deval Patrick leads opinion polls as he aims to be the first Democrat governor of Massachusetts in 15 years.
Minnesota
Popular sitting Republican Tim Pawlenty is in a dog-fight with the
Democrats' Mike Hatch in a race expected to go to the wire.
Nevada
Previously regarded as a lock for Republican Congressman Jim Gibbons, but Democrats are confident they can upset the odds in a race that might be closer than expected.
New York
Eliot Spitzer is expected to cruise to a Democrat victory in New York following Republican incumbent George Pataki's stepping down.
Ohio
Democrat Ted Strickland is poised to end a 16-year Republican stranglehold on the bellwether state, capitalising on a string of local and national scandals.