Excel Cell Alignments: Numerical values for e.g. xlLeft, xlRight or xlCenter?

I've been trying to align Excel cell text values. I've tried the more common xlLeft, xlRight but this doesn't seem to work. The error was xlLeft wasn't declared. I am using Visual Studios and creating a aspx page with VB.

Here is a sample of my code:

    Dim oExcel As Object
    Dim oBook As Object
    Dim oSheet As Object

    'Start a new workbook in Excel
    oExcel = CreateObject("Excel.Application")
    oBook = oExcel.Workbooks.Add

    'Add data to cells of the first worksheet in the new workbook
    oSheet = oBook.Worksheets(1)

    oSheet.Range("A1:E1").Merge()
    oSheet.Range("A1").Value = "Hello"
    oSheet.Range("A2:E2").Merge()
    oSheet.Range("A2").Value = "There "
    oSheet.Range("A1:A4").Font.Bold = True
    oSheet.Range("A1").HorizontalAlignment = -4131