Which is the quickest way to loop through large data sets

Hi,

a general thing: Minimize traffic between VBA and the worksheet
That means: Read the entire sheet with one line into an array and loop there instead of looping through cells, if you want to write data create an array and fill it, then write the entire array to the sheet with 1 line of code

I started to write code, yould you provide a sample workbook?

maybe this works already, if I assigned the sheets correctly:

Option Explicit

Sub GetSAPInfo()
    Dim aData1, aData2, aDataOut, Fuel, Registration
    Dim lRow1 As Long, lRow2 As Long, i As Long, j As Long
    Dim ws1 As Worksheet, ws2 As Worksheet
    Dim Date1 As Date, Date2 As Date
    
    Date1 = DateValue("01/02/2012")
    Date2 = DateValue("01/05/2012")
    
    Set ws1 = Worksheets("Fuel 6050")
    Set ws2 = Worksheets("Vehicles")

    With ws1
        lRow1 = ws1.Cells.Find(What:="*", SearchOrder:=xlRows, SearchDirection:=xlPrevious, LookIn:=xlValues).Row + 1
        aData1 = .Range(.Cells(2, 1), .Cells(lRow1, .UsedRange.Columns.Count)).Value2
    End With

    With ws2
        lRow2 = .Cells.Find(What:="*", SearchOrder:=xlRows, SearchDirection:=xlPrevious, LookIn:=xlValues).Row + 1
        aData2 = .Range(.Cells(2, 1), .Cells(lRow2, .UsedRange.Columns.Count)).Value2
    End With
    
    ReDim aDataOut(LBound(aData2, 1) To UBound(aData2, 1))
    
    For i = LBound(aData2, 1) To UBound(aData2, 1)
        Fuel = 0
        For j = LBound(aData1, 1) To UBound(aData1, 1)
            If aData1(j, 11) = aData1(i, 1) And _
               aData1(j, 7) > Date1 And _
               aData1(j, 7) < Date2 Then
               
                Fuel = Fuel + aData1(j, 5)
                
            End If
        Next j
        aDataOut(i) = Fuel
    Next i
    
    With ws2
        .Range(.Cells(2, 2), .Cells(UBound(aDataOut) + 2, 2)).Value2 = Application.WorksheetFunction.Transpose(aDataOut)
    End With
    
End Sub

try this, runs 0,3 seconds on my machine: Loop through Cells.xlsm

it produces a lot of zeros because of the date restriction, I checked the result only for the 1st entry in Vehicles