Scientific uncertainty is an integral part of the research process and inherent to the construction of new knowledge. In this paper, we investigate the ways in which uncertainty is expressed in articles and propose a new interdisciplinary annotation framework to categories sentences containing uncertainty along five dimensions. We study a corpus of articles from different disciplines and conduct experiments on two different samples of sentences: one sample extracted by uncertainty cue mapping and another sample obtained from manual annotation of randomly selected articles. The two samples are manually annotated using our annotation framework. The results show the distribution of uncertainty types across journals and categories. The samples of annotated sentences can also be used to automate some aspects of the annotation process.