The Internal Revenue Service has announced the new standard mileage rate - 27.5 cents a mile - for the business use of an automobile in 1991. The old 1990 rate was 26 cents per mile.

The new rate, announced Friday, takes into consideration the new five-cents-per-gallon increase in the federal fuel tax and also increased gasoline pump prices.For charitable activities, the standard mileage rate will remain at 12 cents per mile. For medical and moving expense purposes, the 1991 standard rate will also stay unchanged at nine cents per mile. The special standard mileage rate for the business use of an automobile by rural mail carriers will be 41.25 cents per mile in 1991.