HOUSTON, Aug 12 (Reuters) - Midwest cash gasolinedifferentials extended gains on Wednesday on the prospect of amonth-long shutdown of the biggest crude unit at BP Plc's413,500 barrels-per-day (bpd) refinery in Whiting, Indiana,traders said.
Group Three gasoline was seen done at a 30-cent premium toSeptember RBOB futures on the New York Mercantile Exchange, up12.5 cents per gallon from Tuesday's finish.
Chicago gasoline differentials, which gained 50 cents pergallon to finish at a 65-cent premium on Tuesday, were talked ina bid-offer spread of 75 cents/80 cents over futures onWednesday with no deals seen, traders said. (Reporting by Kristen Hays; Editing by James Dalgleish)