The main goal of this paper is to provide a detailed frequency analysis of the five types it is imperative that, it is vital that, it is essential that, it is important that, and it is necessary that within the British National Corpus (100 million, British, 1980s-1993), the Corpus of Contemporary American English (1.0 billion, US, 1990-2019), the Corpus of Historical American English (400 million, US, 1810s-2000s), and the Hansard Corpus (1.6 billion, British Parliament). In this paper, we have examined the frequency of the five types and collected the data. A major point to note is that it is important that was the most preferred by British people, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. The BNC clearly shows, on the other hand, that it is important that was the most commonly used one in the spoken genre, magazine genre, newspaper genre, and academic genre. A further point to note is that it is important that was the most preferred by Americans, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. The COCA clearly indicates that it is important that was the most widely used one in the blog genre, web genre, spoken genre, fiction genre, magazine genre, newspaper genre, and academic genre. The reason why it is important that was the most preferred by Americans and British people in the academic genre may be that a moderate obligation is suitable for conveying factual information. With respect to the COHA, it is worth noting that it is necessary that was the most preferred by Americans from 1810 to 2000, followed by it is important that, it is essential that, it is imperative that, and it is vital that. As for the HC, it is important that was the most preferred by British politicians, followed by it is essential that, it is vital that, it is necessary that, and it is imperative that. It is worth noting that Americans and British politicians show the similar pattern in the ranking of the five types in that Americans did not prefer a strong statement or the strongest statement, whereas British politicians did not prefer the strongest statement.