The abbreviations by superscript letters in 18th century Portuguese are analyzed, with the aim of finding consistent uses by the copyist of abbreviation strategies by superscription. The hypothesis tested is that there are patterns when abbreviating a lexical item, and that the choices made by the copyist regarding the letters that are selected to be overwritten, as well as their quantity, are not random. The corpus used is the Manuscript PBA-749 from the National Library of Portugal, which title is Primeiro copiador das respostas dos senhores governadores desta capitania [minas gerais] às ordens de s[u]a mag[esta]de, e contas que lhe dãoão que principia no governo do sen[h]or Antonio de Albuquerque Coelho de Carvalho. Based on an exhaustive vocabulary of the abbreviations in the document, we selected the 3,793 occurrences of suspension abbreviations. Then, using the theoretical-methodological framework of René Pellén (2005), we examined all the occurrences in depth, looking for rules that could be generalized, thus helping us to better understand not only the brachygraphic system of the time, but also the 18th century Portuguese language. We conclude that abbreviations by superscript letters are not done arbitrarily, and that there are recurring norms and formulas that can be quantified and given generalizing qualitative analyses.