Hi, this code is my code to add a row to an excel file

Code:
Public Sub Add_Records()

        '==========================================================================
        ' Run an INSERT INTO command to add new records to the workbook. 
        '==========================================================================
        Dim Variable As String
        Variable = "15000"
        Dim conn1 As New System.Data.OleDb.OleDbConnection(m_sConn1)
        conn1.Open()
        Dim cmd As New System.Data.OleDb.OleDbCommand()
        cmd.Connection = conn1
        cmd.CommandText = "INSERT INTO [Sales$] (Reference, Customer, Quantity) values (" & Reference & "," & Variable & "," & Quantity & ")"
        cmd.ExecuteNonQuery()
        conn1.Close()


    End Sub
It works fine as long as the variable Variable is a number. If i make it a string it doesnt work. Any ideas why?

Thanks
Alex