I have noticed that different XML files take very different amounts of time to zip, even if the files are of approximately the same size. Sometimes it takes about 7 seconds to zip a 5 megabyte xml file, other times it takes less than a second. It appears to depend on the schema of the file. Here is the code we use to zip, does anything jump out as something that could be improved or changed? The last line, CopyFilesTo(…), is where all the time is taken.