This is why I always write a BOM in CSV files (yes, even though it&#x27;s UTF-8 and it shouldn&#x27;t have a BOM). Excel will actually respect it.<p>The bigger problem is when Excel tries to be helpful and reformats the data upon opening the file. I can&#x27;t remember the intricacies, but it used to behave differently whether you opened it from a local path or directly from a browser. I seem to recall using an &quot;incorrect&quot; MIME type helped with that.