It is not uncommon for many types of modern fighter jets to sustain speeds of one to two times the speed of sound. However, there are a number of jets that are capable of travelling much faster. The world's fastest jet is the X-15, which regularly reached Mach 6.72.
Fifth-generation fighter jets, those that went into production after 2005, are actually considerably slower than many jets from the 1960s and 1970s. Eight of the 10 fastest air crafts on record were developed before 1965, and the fastest jet in the world, the X-15, was first flown in 1959 and retired in 1970.