C# functions with static data

Function EncodeForXml(ByVal data As String) As String
    Static badAmpersand As Regex = new Regex("&(?![a-zA-Z]{2,6};|#[0-9]{2,4};)")

    data = badAmpersand.Replace(data, "&")

    ''// more processing

    return data
End Function

private static readonly RegEx badAmpersand = new RegEx("...");