Opera Mini TM is a mobile web browser. It was developed for mobile phones incapable of running regular web browsers and released globally in January 2006. It has gained great popularity and can be downloaded free of charge to your mobile phone. The Opera Mini client consists of a small Java MIDlet and the only requirement is that your mobile phone support Java ME applications. Opera Mini is a server-client technology. The main benefit of this compared to a regular mobile browser is that all web pages are being pre-processed and compressed in dedicated Opera servers before the information is sent to the mobile phones. This is to make the information more suitable for the small hand held devices as well as to reduce the amount of information transferred to the mobile phones. Opera claims that this technology increases the traffic rates by two to three times, which means better response time and lower cost for the end user. The fact that all traffic is handled by dedicated servers demands for extensive link and server capacity. Opera has a large cluster of Opera Mini servers connected with gigabit links. This is a huge cost for the company.In this thesis we will analyze log files generated from Opera Mini traffic. We will keep main focus on parameters that affects the amount of data transferred to the mobile phones. Our motivation for this choice is that in a regular Opera Mini session, the tight link of the connection will often be the wireless connection between the mobile phone and the mobile operator . This makes the level of compression of the data transferred from the Opera Mini server to the client of great importance for the user experience. Different data types will achieve different level of compression. Some data are more difficult to compress than other. Pictures, already compressed data and encrypted data will not be compressed as much as plain html files or text files . The extensive use of images in web pages is the factor we believe have the greatest impact on the achieved level of compression. In most scenarios the user wants to view images, but the quality of the displayed images is of less importance. The regular Opera Mini user can choose between four different image quality settings in the browser. Our analysis reveal that these settings have impact on the results.