OAuthUrlEncode.cs

public static string OAuthUrlEncode(string s)
{
    if (string.IsNullOrEmpty(s))
    {
        return string.Empty;
    }
    else
    {
        StringBuilder sb = new StringBuilder(s.Length);

        for (int i = 0; i < s.Length; i++)
        {
            if (NoEncodeChars.IndexOf(s[i]) == -1)
            {
                // character needs encoding
                byte[] characterBytes = Encoding.UTF8.GetBytes(s[i].ToString());
                for (int b = 0; b < characterBytes.Length; b++)
                {
                    sb.AppendFormat(CultureInfo.InvariantCulture,
                    "%{0:X2}",
                    characterBytes[b]);
                }
            }
            else
            {
                // character is allowed
                sb.Append(s[i]);
            }
        }

        return sb.ToString();
    }
}