oSheet:Cells(xrow,xx):Value = "
Example:
If you wanted a formula which ADDS then
oSheet:Range("C1" ):Formula = "=A1+B1"
If you wanted a formula which SUBTRACTS then
oSheet:Range("C1" ):Formula = "=A1-B1"
If you want to create a SUM formula then
oSheet:Range("E1" ):Formula = "=sum(A1:D1)"
etc
Anything that you want excel to have you can write as :Formula
Hope that helps