C# 字符串分割

string s = "dsafdfgasd||455565";
            string reg = "||";
             string[] str = Regex.Split(s, reg, RegexOptions.IgnoreCase);
            foreach (string i in str)
                Response.Write(i.ToString());

为什么这样的结果相当于没有分割。

而string s = "dsafdfgasd||455565";
            string reg = "ga";
             string[] str = Regex.Split(s, reg, RegexOptions.IgnoreCase);
            foreach (string i in str)
                Response.Write(i.ToString());