Feb. 3 (Bloomberg) -- Chicago gasoline strengthened after BP Plc shut a fluid catalytic cracker for unplanned repairs at the Whiting refinery in Indiana.

The unit is one of two catalytic crackers at the 420,000- barrel-a-day plant, according to a person familiar with refinery operations who declined to comment because the information isn’t public.

The discount for conventional, 87-octane gasoline in Chicago narrowed 5.5 cents to 14.5 cents a gallon versus futures traded on the New York Mercantile Exchange at 12:52 p.m. The fuel has strengthened from a discount of 33 cents on Jan. 24. Prompt delivery rose 8.46 cents to $2.7535 a gallon.

The same fuel in New York Harbor held at a premium of 1.88 cents to futures. Prompt delivery rose 2.41 cents to $2.9118 a gallon.

Sunoco Inc. reported that a compressor associated with a reformer in the Girard Point section of the Philadelphia refinery lost power yesterday, according to a filing with city regulators. Power was restored before the unit was shut down, the filing showed.

--With assistance from Lynn Doan in San Francisco. Editors: Charlotte Porter, Richard Stubbe

To contact the reporter on this story: Paul Burkhardt in New York at pburkhardt@bloomberg.net.

To contact the editor responsible for this story: Dan Stets at dstets@bloomberg.net.