UPS uses an index-based surcharge that is adjusted weekly. Changes to the surcharge will be effective on Monday of each week. The surcharge will be based on the National U.S. Average On Highway Diesel Fuel Price as reported by the U.S. Energy Information Administration (EIA) for the week that is two weeks prior to the adjustment, rounded to the nearest cent. For example, the surcharge for the week of February 6, 2017 is based on the National U.S. Average On Highway Diesel Fuel Price for the week of January 23, 2017.
https://www.ups.com/be/en/support/shipping-support/shipping-costs-rates/fuel-surcharges.page#link1