A win in the Beaver State will give the Illinois senator the larger share of the state's 52 delegates.

With 40 percent of precincts counted, Obama lead Clinton 59 percent to 41 percent, CNN reported.

Obama, with a victory in Oregon, has an almost insurmountable lead over Clinton in the race for delegates.

Obama is expected to pick up at least 14 delegates from the Kentucky primary he lost to Clinton by 35 percentage points.

A CNN tally indicates those delegates would give him 1,627 of the 3,253 pledged delegates at stake in all of the state's primaries and caucuses.

A candidate needs 2,026 delegates to clinch the party's nomination. Since neither candidate can amass that number, the party's superdelegates—party leaders and elected officials—will choose who will be at the top of the Democratic ticket.