Abstract: Affected by the global COVID-19 and middle/low oil prices, the exploration investment has been running at a low level and the exploration workload has fallen in 2021. However, oil companies have focused on frontier exploration fields and key areas of exploration and development. Through deepening geological understanding and improving trap identification ability, the success rate of exploration has continued to be improved. Offshore exploration, especially deepwater and ultra-deepwater large discoveries, continues to emerge, and major international oil companies are responsible for the discovery of transnational giant and medium-sized oil and gas fields, which is mainly located in "one ocean, one bay and one sea" (both sides of the Atlantic Ocean, the Gulf of Mexico and the southern Caspian Sea). Through the analysis of deepwater and ultra-deepwater typical oil and gas fields, three characteristics are summarized. Firstly, by paying close attention to the oil and gas bearing basin, a series of pre-salt oil and gas discoveries were made in Brazil after an interval of eight years. Secondly, by accumulating knowledge and strategic return, Eni has successively found oil fields in the Cote d'Ivoire basin. Thirdly, by development first and expanding the surrounding areas, bp has found giant fields in the South Caspian Sea. In view of the practice of the major international oil companies in carrying out transnational deepwater and ultra-deepwater exploration, three enlightenments are summarized. Firstly, farming in in advance,in the way of seizing the favorable exploration domains, and flexibly farming in and farming out. Secondly, following the strategy, constantly accumulating experience and technology to steadily improve strength. Thirdly, Independent exploration, mastering key core technologies to achieve exploration efficiency. Chinese oil companies still need to seize all opportunities to actively obtain favorable exploration blocks, form effective reserves of resources, and realize the leap from "going out" to "going up" through "one transformation and three strengthening".