Technical investigation of accidents and incidents is carried out in order to establish the technical and organizational causes of accidents at hazardous production facilities. The legislation of the Russian Federation established the mandatory nature of this procedure, which is regulated by Order № 503 adopted by Rostechnadzor. This regulatory document describes the procedure for conducting an investigation and other organizational issues, but there is no more detailed information on the distribution of causes by groups. As the analysis of the materials of such investigations conducted by the authors of this article shows, there is a problem of uniformity in their identification (various experts formulate the causes of accidents and classify them as technical or organizational in different ways, based on their education, their own experience and other factors). Having analyzed more than 100 «lightnings» (information sheets indicating the causes after an accident investigation), posted on the official website of Rostechnadzor in the section Lessons learned from accidents, the authors of the article found some inconsistencies in assigning causes to a specific group, for example, the causes those related to strictly technical ones were correlated with the group of organizational ones. In this regard, there is a need to adopt an appropriate regulatory legal act, which in its content would have a clearer and, as far as possible, detailed classification of the causes of accidents and incidents for hazardous production facilities in the oil and gas industry. In order to ensure the unity of formulations of the causes of accidents and incidents by different experts and to facilitate their machine processing, a draft classification of them is proposed, set out in the article.