System 2.0.0.0 4.0.0.0 System.Enum This enumeration is used with the and classes. Specifies whether to compress or decompress the underlying stream. Field 2.0.0.0 4.0.0.0 System.IO.Compression.CompressionMode Compresses the underlying stream. Field 2.0.0.0 4.0.0.0 System.IO.Compression.CompressionMode Decompresses the underlying stream.