Function URLEncode(Data As String, ParamArray Exceptions() As String) As String
  Dim buf As String
  For i As Integer = 1 To Data.Len
    Dim char As String = Data.Mid(i, 1)
    Select Case Asc(char)
    Case 48 To 57, 65 To 90, 97 To 122, 45, 46, 95
      buf = buf + char
    Else
      If Exceptions.IndexOf(char) > -1 Then
        buf = buf + char
      Else
        buf = buf + "%" + Left(Hex(Asc(char)) + "00", 2)
      End If
    End Select
  Next
  Return buf
End Function

 'usage
 Dim s As String = URLEncode("http://foo bar/") ' no exceptions
 Dim t As String = URLEncode("http://foo bar/", "!", "?", ",") ' with exceptions