1. Big project
2. An example workbook would help, along with some worked 'examples'
3. Excel's Scenario Manager might be able to do it without VBA
4.The easiest way might be to have a list of the gas prices, and a loop that uses each price on the other sheets to calculate, and then put the results on the Summary sheet
The attachment has a simple example for some made up gas prices and dummied up data
Option Explicit
Sub Demo()
Dim i As Long
Application.ScreenUpdating = False
With Worksheets("Summary")
For i = 2 To .Cells(1, 1).CurrentRegion.Rows.Count
Worksheets("E_current_no").Range("A2").Value = .Cells(i, 1).Value
Worksheets("E_current_with").Range("A2").Value = .Cells(i, 1).Value
Application.CalculateFull
.Cells(i, 2).Value = Worksheets("E_current_no").Range("N3").Value
.Cells(i, 3).Value = Worksheets("E_current_with").Range("N3").Value
Next i
End With
Application.ScreenUpdating = True
MsgBox "Done"
End Sub
There are other (and more elegant) ways to do it