I agree with LCruiser, it's not realstic to to come up with the actual fuel usage on the project, how about making an estimate of what the total fuel usage will be per CY for the specific project and list the assumption in your spec, then also tie an adjustment to a fuel price index. Use a spec similiar to the one I referenced above but modify it to read as follows:
Total payperiod adjustment = AQ
For an increase in average cost per gallon of diesel during the pay period which exceeds 10 percent of that at bid time:
A = (Iu/Ib - 1.10) Ib
For a decrease in average cost per gallon of diesel during the pay period which exceeds 10 percent of that at bid time:
A = (Iu/Ib - 0.90) Ib
Where:
A = Adjustment in dollars per gallon of diesel used (rounded to the nearest $0.01.)
Iu = The average of the weekly prices reported as “Average Weekly Retail Price per gallon of Diesel” for the ____ Region, as published by U.S Government, Department of Energy, Energy Information Administration (
which were in effect during the pay period, regardless of rates of work proceeding during the pay period.
Ib = The “Average Weekly Retail Price per gallon of Diesel” for the ____ Region as published by U.S Government, Department of Energy, Energy Information Administration (
on the nearest date preceding or coinciding with the official bid date opening.
Q = Quantity in gallons of diesel that was used during pay period. Said quantity shall be determined by multiplying the quantity in cubic yards of Bid Item XX REPLACE PORTLAND CEMENT CONCRETE PAVEMENT paid for during the period by the factor of xx.xx gal diesel/CY. (comment: Design / Spec Writer to provide a realistic value for the average quantity of fuel needed for the bid item.
The above spec puts any risk of fuel price changes in excess of 10% on the owner. If they go down 15% from what they were at bid time, the owner gets credit for the 5% difference, and visa-versa if they go up. If you want to change the 10% contractor's risk window, change the 1.10 and 0.90 factors respectively.