here in new england the price of diesel bounces around depending on season and temperatures.
in moderate times of the year diesel is about 30 cents more. In colder times i have seen-you won't believe this -a dollar difference per gallon. this is usually in cold winter months.
However based on mileage of diesel it's probaby overal closer to break even.
the switchover to ulsd in 2007 combined with the new emissions equipment now required(dpf,def) has brought the diesle advantage over gas closer together.