Thirteen epistles have been attributed to Paul: Romans, 1 Corinthians, 2 Corinthians, Philemon, Galatians, Philippians, 1 Thessalonians, 2 Thessalonians, Ephesians, Colossians, 1 Timothy, 2 Timothy and Titus. Hebrews was also at one stage attributed to him, but that is clearly not the case. It was never attributed to him until late in the second century.
Scholars attribute seven of these epistles to Paul, and of these five have been shown by computer analysis to contain exactly the same writing or dictation style: Romans, 1 and 2 Corinthians, Philemon and Galatians. The two that may, with some confidence, be attributed to Paul, but do not match the style of Galatians are Philippians and 1 Thessalonians.