I don't know if there is a standard, but the average is only about $0.30 per mile. Some more, some less. You can ask HR to find out what they pay where you work.
According to the American Automobile Association, an average car driven 15,000 miles a year, the true cost is closer to 56 cents a mile – and this is before Hurricane Katrina raised fuel costs even further.
The last time I heard it was 43 cents per mile.