GZipStream, compressed date differs in size

I am using GZipStream for compression, and the size and contents of
the compressed byte array differs from time to time, using the same
source.
>
byte[] uncompressed = Enc.GetBytes(xmlNode.OuterXml);
byte[] compressed = compress(uncompressed);
>
private byte[] compress(byte[] uncompressed)
{
MemoryStream ms = new MemoryStream();
GZipStream gzStream = new GZipStream(ms,
CompressionMode.Compress);
gzStream.Write(uncompressed, 0, uncompressed.Length);
gzStream.Close();
return ms.ToArray();
}
>
Length of uncompressed data is 89368.
Running this a couple of times results in comressed length of
20260-20263, with different contents.
Decompression of the resulting byte array works fine i all cases
though.
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Is this expected behavior?
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// HÃ¥kan
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