By John Dodge

CHICAGO (CBS) — Gasoline prices in Chicago are at their highest levels in six months.

The average price for a gallon of regular unleaded gasoline is $3.89, nearing the six-month high of $3.92 in early September.

A gallon of gasoline has risen more than 50 cents in the past three months.

Prices in the past six months were at their lowest, in early December at $3.35.

Outside of about six cities in California, such as San Francisco ($3.92) and Los Angeles $3.93, and Honolulu ($4), Chicago’s prices are the highest in the country, according to Gas Buddy.

Local taxes account for much of the reason behind high prices here. In Northwest Indiana, for example, prices run about 20 to 25 cents less.

The national average is $3.44 a gallon.

Supplies have been reduced in the Midwest in recent days as refineries move out their winter gasoline in preparation for warmer weather ahead, according to Energy Information Administration. That is one reason prices are up. Demand is also up slightly.

On Monday, oil jumped more than $2 to $104.75 a barrel, its highest level since last September.

The spike came as concern that unrest in Ukraine could disrupt global supplies from Russia–one of the world’s largest oil producers.

President Obama over the weekend told Russian President Vladimir Putin to move Russian forces back to bases in the southern region of Crimea and to refrain from any interference elsewhere in Ukraine.

Ukraine’s government was overthrown following violent protests last month and there are fears that continuing violence could lead to civil war. Russia moved its forces a few days after the change in government there.