Back in 1981 when the fuel prices went nuts,and there were many other issues,the trucking industry had a 2 week shut down.At the end of the shut down,weights went to 80000 lbs,larger trailers,48ft lol,and a fuel surchatge.At that time,the formula was for every penny over a 1.15/gallon,devided by 5 mpg there would be a surcharge to the owner or whom ever was paying for the fuel.Since that time,most carriers pay a fuel surcharge if the fuel costs dictate to it,and the feds say its ok.
Last year where i lease my truck, they changed the way we were getting paid,as many of our customers would not pay the surcharge.Originally we were getting a percentage of the gross pay for the surcharge,now we get a flat rate per mile,each week when the national average of fuel changed,our fsc also changes.It is set that we never pay more than $1.20 per gallon,and each size unit is based on there miles per gallon,for me thats 6 mpg,but since i get closer to 7 mpg,and sometimes even more,my actual fuel costs are less than the $1,20
hope this helps.Just remember,whom ever pays for the fule is to get the fsc